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
If you are using VSCode and Windows.
VSCode
Windows
1.Press Control + Shift + F.
Control + Shift + F
2.Find Your Package Name and Replace All with your new Package Name.
Package Name
Replace All
new Package Name
type "cd android"
"cd android"
type "./gradlew clean"
"./gradlew clean"