To change monitor notification settings for Android phones, launch GDB monitor app, tap the device in ‘My Devices’ view, then tap ‘Device Reminder Settings’.
For Android 8 or newer OS, The sound change setting for your phone is not in GDB monitor app’s settings. It is in your phone’s settings. Launch ‘settings’ app from your phone > Apps > GDB monitor > Notifications > Tap ‘Push notifications’ text(not tapping the switch) > Sound > select your sound.