are you referring to the wired headset?? if so he needs to turn up the volume on the phone itself. while on a call. i believe on the right side of the phone there are the up and down arrows. while on a call push up. he will see the volume indicator on the call screen increase and he should hear the volume increase on the headset. if its a bluetooth, the bluetooth itself will have a volume up and down, if thats the case have him look in the owners manual for the bluetooth