Hi Duncon,
This is from memory, it’s been a while since I had bass pedals.
The switch in the back is correct.
The pedals must be assigned to a part setting.
1-Press program Menus (Right side)
2-Press Sound.
3-Press Part setting
4-(Top left) Arrows you will use to scroll though the different parts.
5-Select a part – the type of bass to be used and volume. There are also other areas if you wish. Then set what you have done in a Registration and Bank.

Each time you use the pedals and press that registration you will have what you want.
Important – You must put the set-up in every registration you use, it does not always have to be the same bass or volume.

I hope this helps, John C.