diff --git a/.changeset/public-masks-kiss.md b/.changeset/public-masks-kiss.md
new file mode 100644
index 0000000..f97be8f
--- /dev/null
+++ b/.changeset/public-masks-kiss.md
@@ -0,0 +1,5 @@
+---
+"@webiny/data-transfer": patch
+---
+
+Fix `.env` population for older scaffolded projects: `writeEnv` now supports plain `KEY=value` `.env.example` files by uncommenting commented-out known keys and appending missing ones. Config template auto-enables OpenSearch when the env vars are set — no manual uncommenting needed.
diff --git a/__tests__/commands/transfer/wizard/envWriter.test.ts b/__tests__/commands/transfer/wizard/envWriter.test.ts
index d24c3f0..f6018d6 100644
--- a/__tests__/commands/transfer/wizard/envWriter.test.ts
+++ b/__tests__/commands/transfer/wizard/envWriter.test.ts
@@ -176,7 +176,40 @@ describe("writeEnv", () => {
         await writeEnv(tmpDir, values);
 
         const content = await readFile(join(tmpDir, ".env"), "utf8");
-        expect(content).toBe("TARGET_OS_INDEX_PREFIX=\n");
+        expect(content).toContain("TARGET_OS_INDEX_PREFIX=\n");
+        expect(content).not.toContain("old-prefix");
+    });
+
+    it("plain format uncomments commented-out known keys and fills them", async () => {
+        const plain = [
+            "SOURCE_REGION=eu-central-1",
+            "# SOURCE_OS_TABLE=",
+            "# TARGET_OS_TABLE=",
+            "# TARGET_OS_ENDPOINT="
+        ].join("\n");
+        await writeFile(join(tmpDir, ".env.example"), plain);
+
+        await writeEnv(tmpDir, SAMPLE_VALUES);
+
+        const content = await readFile(join(tmpDir, ".env"), "utf8");
+        expect(content).toContain("SOURCE_OS_TABLE=wby-source-es");
+        expect(content).toContain("TARGET_OS_TABLE=wby-target-os");
+        expect(content).toContain("TARGET_OS_ENDPOINT=search-target.us-east-1.es.amazonaws.com");
+        expect(content).not.toContain("# SOURCE_OS_TABLE");
+        expect(content).not.toContain("# TARGET_OS_TABLE");
+    });
+
+    it("plain format appends missing known keys at the end", async () => {
+        const plain = "SOURCE_REGION=eu-central-1\nSEGMENTS=4\n";
+        await writeFile(join(tmpDir, ".env.example"), plain);
+
+        await writeEnv(tmpDir, SAMPLE_VALUES);
+
+        const content = await readFile(join(tmpDir, ".env"), "utf8");
+        expect(content).toContain("SOURCE_REGION=eu-central-1");
+        expect(content).toContain("SEGMENTS=8");
+        expect(content).toContain("TARGET_OS_ENDPOINT=search-target.us-east-1.es.amazonaws.com");
+        expect(content).toContain("SOURCE_ACCOUNT_ID=111111111111");
     });
 
     it("uses built-in template when .env.example is absent", async () => {
diff --git a/src/commands/transfer/wizard/envWriter.ts b/src/commands/transfer/wizard/envWriter.ts
index 3bb0d1c..9d8adc2 100644
--- a/src/commands/transfer/wizard/envWriter.ts
+++ b/src/commands/transfer/wizard/envWriter.ts
@@ -79,25 +79,38 @@ function substituteTokens(template: string, values: EnvValues): string {
 }
 
 function substituteEnvLines(content: string, values: EnvValues): string {
-    return content
-        .split("\n")
-        .map(line => {
-            const trimmed = line.trimStart();
-            if (!trimmed || trimmed.startsWith("#")) {
-                return line;
-            }
-            const eqIndex = trimmed.indexOf("=");
-            if (eqIndex === -1) {
-                return line;
-            }
-            const key = trimmed.slice(0, eqIndex).trim();
-            const envKey = TOKEN_MAP[key];
-            if (envKey) {
-                return `${key}=${String(values[envKey])}`;
-            }
+    const seen = new Set<string>();
+    const lines = content.split("\n").map(line => {
+        const trimmed = line.trimStart();
+        if (!trimmed) {
             return line;
-        })
-        .join("\n");
+        }
+
+        const commented = trimmed.startsWith("#");
+        const stripped = commented ? trimmed.slice(1).trimStart() : trimmed;
+        const eqIndex = stripped.indexOf("=");
+        if (eqIndex === -1) {
+            return line;
+        }
+
+        const key = stripped.slice(0, eqIndex).trim();
+        const envKey = TOKEN_MAP[key];
+        if (envKey) {
+            seen.add(key);
+            return `${key}=${String(values[envKey])}`;
+        }
+        return line;
+    });
+
+    const missing = Object.entries(TOKEN_MAP).filter(([key]) => !seen.has(key));
+    if (missing.length > 0) {
+        lines.push("");
+        for (const [key, envKey] of missing) {
+            lines.push(`${key}=${String(values[envKey])}`);
+        }
+    }
+
+    return lines.join("\n");
 }
 
 export async function writeEnv(projectDir: string, values: EnvValues): Promise<void> {
diff --git a/templates/projects/example/config.ts b/templates/projects/example/config.ts
index e7e3077..5cc6fc0 100644
--- a/templates/projects/example/config.ts
+++ b/templates/projects/example/config.ts
@@ -8,27 +8,30 @@ import {
 
 loadEnv(import.meta.url);
 
+const sourceOsTable = fromEnv("SOURCE_OS_TABLE", null);
+const targetOsTable = fromEnv("TARGET_OS_TABLE", null);
+
 export default createConfig({
     source: {
         region: fromEnv("SOURCE_REGION", "eu-central-1"),
         credentials: fromAwsProfile({ profile: fromEnv("SOURCE_PROFILE", "default") }),
         dynamodb: { tableName: fromEnv("SOURCE_DDB_TABLE") },
-        s3: { bucket: fromEnv("SOURCE_S3_BUCKET") }
-        // Uncomment if your Webiny project uses OpenSearch:
-        // opensearch: { tableName: fromEnv("SOURCE_OS_TABLE") }
+        s3: { bucket: fromEnv("SOURCE_S3_BUCKET") },
+        opensearch: sourceOsTable ? { tableName: sourceOsTable } : null
     },
     target: {
         region: fromEnv("TARGET_REGION", "eu-central-1"),
         credentials: fromAwsProfile({ profile: fromEnv("TARGET_PROFILE", "default") }),
         dynamodb: { tableName: fromEnv("TARGET_DDB_TABLE") },
-        s3: { bucket: fromEnv("TARGET_S3_BUCKET") }
-        // Uncomment if your Webiny project uses OpenSearch:
-        // opensearch: {
-        //     endpoint: fromEnv("TARGET_OS_ENDPOINT"),
-        //     tableName: fromEnv("TARGET_OS_TABLE"),
-        //     service: "opensearch",
-        //     indexPrefix: fromEnv("TARGET_OS_INDEX_PREFIX", "")
-        // }
+        s3: { bucket: fromEnv("TARGET_S3_BUCKET") },
+        opensearch: targetOsTable
+            ? {
+                  endpoint: fromEnv("TARGET_OS_ENDPOINT"),
+                  tableName: targetOsTable,
+                  service: "opensearch",
+                  indexPrefix: fromEnv("TARGET_OS_INDEX_PREFIX", "")
+              }
+            : null
     },
     pipeline: {
         segments: numberFromEnv("SEGMENTS", 4),