Audio doesn't re-route to bluetooth earphone

I am facing a problem with audio. Every time when Bluetooth headset/earphone is disconnected from the app, background music in the app stops playing. It is supposed to re-route to the phone speaker. Is there any workaround for this?

I figured that when connecting or disconnecting Bluetooth, the app loses audio focus. I need help to regain focus and resume audio. Does anyone know how to regain focus in the unity app?

Target Platform: Android Unity Version: 2019.4.20f1