a) Make sure the volume is adjusted from all possible options. Like- Music streaming APP/Video APP/Mobile Phone and TWS
b) Use the device with different mobile phones and check if a particular song or video has the issue
c) Clean the ear tips in case there is cerumen inside the ear tips
d) In case there is low sound during call, then there might be network issue or other side user's mobile phone or BT device might have the issue
 e) Try to reproduce the issue with different Mobile phones and different APPs.