How to update version number of react native app

You should be changing your versionCode and versionName in android/app/build.gradle:

android {

    defaultConfig {

        versionCode 1
        versionName "1.0"
        
        {...}
    }

    {...}
}

Note that versionCode has to be in an integer that is larger than the ones used for previous releases while versionName is the human readable version that may be shown to users.