Guidance v Music Volume in Carplay

Someone brought this up before, but it was not resolved.

1-Using Carplay with iPhone 11.

2-Listening to a book with Audible.

3-Ask SIRI for directions.

4-End navigation.

5-Now car volume controls only affect Guidance Volume (even though I'm no longer using navigation). I can't turn book volume or radio volume up or down.

6-The problem is intermittent, but--when it happens--I have to turn off the car and unplug the phone. When I restart, the problem may or may not be solved.

>>Using Carplay, how do I select which volume I want to control?