Lots of good advise.
My input......The problem is one of two thngs
1) The electrical valve controller is not working strong enough or not at all
2) The electrical valve controller is working properly, but cannot budge a stuck valve
If the controller "Is" working properly, it should move at least a tiny bit until it stops against the stuck valve hardware. If you see the controller move only a tiny bit, get under there and grab the valve handle too, and help it along.
If the controller is determined to be dead, check the wiring. Failure is likely due to corrosion on crimped wire connections. Clean all internections, best to solder them together and insulate them with shrink tubing.
If I determined my valve controller is not working, I would apply 12v directly to it, and ground directly from it, to bypass the electrical system just to see if it works properly all by itself. If it does not work, reverse polarity to get it to reverse direction. If still nothing happens, then replace it. You could test it easily once it is removed from the RV. Just touch the two wires across the chassis battery one way, then reverse the wires to get it to move in the opposite direction. If it is not moving right, buy a new one.