How to debug the Android App in release mode using Android studio

In your gradle file, you must add debuggable ability in your release flavor.

buildTypes {
    release {
        debuggable true
        minifyEnabled false
        signingConfig signingConfigs.release
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
    }
    debug {
        debuggable true
        minifyEnabled false
        applicationIdSuffix '.debug'
    } 
}

signingConfig is release configuration it must be added in gradle file in android{} block, something like this:

signingConfigs {
    release {
        keyAlias 'YourAppKey'
        keyPassword 'somePassword'
        storeFile file('appkeyfile.jks')
        storePassword 'somePassword'
    }
}