Is it a Schwintek slide? It'll have 2 tracks on either side, 2 motors and a controller to keep them in sync. The tracks look like this:
If so, the "override" sucks. You have to disconnect power to the motor. You can either get access to the motor by pulling down trim and a gasket and then unplugging the wire harness to each. Or, you should be able to disconnect the battery (and shore power). And then PPPPUUUUSSSSSHHHHHH.
I bruised my shoulders from pushing before I found that if I squatted, I could push with my legs with my back against the slide. I also found that the linoleum flooring wanted to shift from it. So I would have my wife stand in front of me and I'd plant my feet. Also using my arm to push against a doorframe helped.
The biggest thing is you need to get access to the controller and inspect its flashing lights/codes.
If it isn't a Schwintek, none of this is helpful.