Before uploading the release build to the Play Store, 
make sure you test it thoroughly. 

mkdir -p android/app/src/main/assets
react-native bundle --platform android --dev false --entry-file index.js --bundle-output android/app/src/main/assets/index.android.bundle --assets-dest android/app/src/main/res
react-native run-android --variant=release

Export Apk -
cd android && ./gradlew bundleRelease -x bundleReleaseJsAndAssets

- Your AAB BUNDLE will be present in the folder
/android/app/build/outputs/bundle/release