Bypass valves are usually BEHIND the water heater where all the plumbing pipes are located, unless you have a plumbing station. Not being familiar with your particular RV, You may have to remove a panel, go thru a kitchen cabinet, drawer, etc to access them. Since you know where the water heater is located on the outside of your RV, you can go inside the RV and try to figure out how to gain access to the rear of it.
You may have a 1, 2, or 3 valve system. If the 3 valve system, you need the valves set like below for normal use:
No matter the amount of valves, you don't want the cold water in to mix with the hot water out......and need to make sure the "bypass" valve is in the completely off position that ties the two pipe systems together.