Seems like the volume control button on my bluetooth headset is broken, is there any way to change the bluetooth volume directly on the phone? I am on Android 4.1.2, just in case it's relevant. I found settings to change the normal front speaker volume, but nothing for the bluetooth volume.
See if this helps. I am not sure though:
Settings >> Sound >> Volumes
If this doesn't help try this Bluetooth Volume app. This should do it.