Hi,
not sure if react-native works the same way like the native Android/ Java approach but in the java Android API there are two classes you have to adapt
audio\WebRtcAudioTrack.java (change every related STREAM_VOICE_CALL to STREAM_MUSIC)
audio\WebRtcAudioTrack.java (change every related STREAM_VOICE_CALL to STREAM_MUSIC)
if that doesn't work you might need to compile the lib webrtc youself and change
modules/audio_device/android/opensles_player.cc
sdk/android/src/jni/audio_device/opensles_player.cc
Just search for SL_ANDROID_STREAM_VOICE and change it to SL_ANDROID_STREAM_MEDIA.
Like I said I'm using webrtc in my native Android/ Java app and it works there. Could be that you must do something different for react-native