This is one of those times when we might be better to let the pros do the fix as it can get kind of tricky simply getting to the right parts.
I see two tracks on the top and bottom of the slide and there is likely a matching set on the far side.
There are usually two small motors one on each end with shafts that go up and down to hold smallish gears on the track. Those motors and gears turn forward or back to move the slide.
What can happen is there is some small twist in the slide or some reason for one gear to get somewhat off track and begin to bind and make noise. A some point that dragging/misalignment gets too much and some part in the linkage from top or bottom gear breaks. When one breaks it puts more strain on the other one on that motor and it then often breaks as well. A lot of times we wind up one side moving but not the other but in your case is sounds like the top two may have broken and not moving to get it crooked top to bottom instead of left to right.
I've never been bold enough to try to find a way into those motors but videos of doing it make it seem the motor is just pretty easy to swap out but getting the slide to thr right position and taking the correct trim off to find the motor is not something I've tried.
If you pull the inside rubber flap back, you may be able to spot the motor inside a channel when inside with the slide partly extended.
Lots of videos of folks doing the job, but I'm one to pass on this job!
But to move it when needed, this may work.
As somebody presses the switch a couple strong folks on the outside may be able to "walk" each end until they get the whole unit moved in. Kind of like pushing a cork into a bottle when it is tight? The motors may still be trying to move one part, so if you push at the right time and place to move the other part, it may work out?
Hit switch as you push, wiggle, push switch again?
At some point this can overheat the breaker or fuse on the slide, so knowing where this is and replacing it may be helpfull.
But then you may get lucky and it slides like greased!! I will wish you luck on that.
Once in, there is often a way to lay 2X4 on top of the slide to press against the trim and wall to make sure it can't go back out suddenly.