Howdy. So in reviewing the manual for the Atwood propane water heater model on our 2016 rig I founds out that it is an electric model as well but the electric switch on the DSI panel in the trailer ...
Look at the breakers in your electrical panel in your TT. If your heater is wired there should be a separate circuit breaker for the "electric side" of your heater labelled as such AND a toggle switch somewhere in the galley to turn on the electric. Otherwise what was said earlier is the case - you have a gas-only model and it's not likely it can be upgraded to include an electric heating element.