The M.H. that I have, has a slide out and a long handle crank also Tobe used when the electric will not bring it in or out.
I have had to use it about 4 times in the past the reason was elect connection was working now and then so I had it connected to a different electric power.
In order for me to move the slide in or out I had to open up a compartment door under the slide and expose the motor, now on the bottom of and in back of the motor their is a lever that hangs down and if you push it in one way or the other because it will only move in one direction to disengage it from the rail or track then you should be able to move the slide in or out with the crank.
If you have it in or out and to keep it from moving flip the lever on the motor in the other direction.
The area that you connect the crank to could be on the other side of where the motor is.
If the motor is on the left side of the slide then the cranking area should be on the right side.
It your still are having trouble with it I would take it to a 5-wheel shop they work on slide all the time.
Just a thought.