To control the volume of the treble or bass sound, select TREBLE or BASS in Sound Settings, and then adjust the volume between -6~+6 by using the Up/Down buttons. The Sound Settings button is the little cogwheel on the right of your remote.
If this doesn't work, then we'd advise attempting to pair the Sub again. I pulled this from your manual on manually pairing the two:
Let us know if you manage to get all that bass!
Welcome to the Community! :smileyhappy: