Hi,
There is an entry in the FAQ about it, but I can’t find that config, has it disapeared ??! (App version 3.0.7)
Changing the Voice or Amplify the Volume
Amplify using different channels
For example if you want to listen to music while navigating, you can choose the output channel for the navigation. Go to the Settings → Navigation → Voice guidance output, and select the output channel. Your options are: media, phone, and notification. You could set it to phone. This allows you to modify the volume for each channel separately.