BB I have a year older coach with a similar setup.
I have a single toggle switch on the left driver's side panel. That switch is either on or off. Forward is on, rearward is off. I think the light changes color when switched on, but do not remember. There are not two settings for this brake.
Look up near your turbo and you should see the exhaust brake cylinder that controls the butterfly valve in the exhaust piping. You will need to lubricate the pivot points here occasionally with high temp lube.
My brake is a Pak Brake exhaust brake.
The exhaust brake when turned on will function between 30 and 60 mph.
Go to the Pak Brake website for instructions.
1995 CC Magna #5280
C8.3L 300hp Cummins, 31,000lbs