Assuming the glass is still in the rubber glass run?
If you grab the arm is it movable in the track, even slightly, ie: check that the wheel is in the track and not stuck (it doesn't appear to be out of the track).
With your head close to the regulator what do you see and hear when you press the window switch? ie: click and nothing, or click and the arm tries to move then nothing??
Point is, if the arm isn't stuck or wheel out of the track, then it could be a dead motor. Only thing to do is to first tape the window in place, run a couple long strips of a strong tape up and over the door frame sticking to both sides of the glass to hold the window up.
Then unbolt the regulator from the door (4-10mm bolts), disconnect the motor harness, and pull the regulator with motor out of the door cavity via
the large opening.
(Tip: stuff a roll of paper towels in the bottom of the door cavity while the regulator is out, that will cushion the fall if the tape lets loose and drops the glass)
Once you have the regulator in your hand inspect for damage then hook the power back up to the motor and push the switch to see if the regulator-motor moves. Don't get your fingers in the way of any moving parts.
Photo shows a new left side rear door regulator and new motor siting on the rear seat. In the background (left, lower) is the door switch and harness. For those with eagle eyes, the last screw to mount the new motor has not yet been installed, the arm had to be moved to gain access to the screw hole.
Edit: I missed the part that you can reposition the glass then it will go up??