I used react-native init MyApp to initialise a new React Native app. This created among others an Android project with the package com.myapp.
react-native init MyApp
com.myapp
After running this:
react-native-rename "MyApp" -b com.mycompany.myapp
Make sure to also goto Build.gradle under android/app/... and rename the application Id as shown below:
Build.gradle
android/app/...
defaultConfig { applicationId:com.appname.xxx ........ }