If you have a cupholder in the passenger side arm rest, try pulling it and see if you can see the back side of the doorbell. If you can, but can't get to it thru the cupholder hole, you will probably have to take off the switch panel to access it.
I suspect it is nothing more than a momentary push button. You may be able to take it to Home Depot and find a similar if not exact replacement. You might have to buy an outdoor assembly and remove the button part from the housing, but I'll bet you can find something that will work.
Isn't your actual doorbell located in the coach, somewhere? Ours is high on the wall of the cabinet under the vanity sink.
Not knowing exactly you your coach is configured, that would be my suggestion.
Jim & Angie, Boise, ID
2006 Monaco Dynasty Countess III
2017 GMC Acadia Denali