Request to mute the incoming calls on the JustCall Mobile app

User is currently using JC on Android App and is looking to get the calls coming on the app to be muted. Changing the sound settings on the phone affects all the applications on the phone and hence he is looking to get this available for only the JustCall Mobile app.
Business use case shared :
They have client meetings and attend sensitive appointments where business calls are not welcome. In the evening and at night, they would prefer to silence the call rather than hang up on a client if they cannot take the call (e.g., when with family, etc.).