1Before uploading the release build to the Play Store, 
2make sure you test it thoroughly. 
3
4mkdir -p android/app/src/main/assets
5react-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
6react-native run-android --variant=release
7
8cd android && ./gradlew bundleRelease -x bundleReleaseJsAndAssets
9
10- Your AAB will be present in the folder
11<project>/android/app/build/outputs/bundle/release

1Genrate Keystore File ->
2keytool -genkeypair -v -storetype PKCS12 -keystore my-upload-key.keystore -alias my-key-alias -keyalg RSA -keysize 2048 -validity 10000
3

1 cd android && ./gradlew assembleRelease