First time motorhome buyer where is the water heater bypass?

The bypass valves are typically located at the back of the water heater. Check the area inside where it's located for access via a cabinet, a removable panel in a closet, removing a drawer, or possibly a removable decorative panel. Setting the valves to the bypass position is normally one of the first steps in winterizing with RV antifreeze, so none goes into the heater tank. The tank just needs to be drained.