Depending on where the damage is, it won't work in all probability. The sides are triple skinned and there's no practical way through for the majority of the outer skin. There is one small hole on the inner skin near the seat belt reel, but that will only allow you to get through to a small area of the outer skin adjacent to the door.
If you want to go ahead -
Remove the rear seat base ( 2 10mm nuts in the footwell )
Undo the two allen head bolts fixing the side panel to the floor
Remove the plastic rivet halfway up at the rear bulkhead.
Remove the sill cover in the door aperture ( just lift off )
Pull the rubber door seal off where it encounters the rear panel.
Now comes the difficult bit and the point at which damage can occur -
The top of the panel is held to the car body by three plastic rivets in a row under the rear window. There is a real risk of damaging the rear panel getting these off. Gently pull the bottom of the panel away from the car and look behind the panel with a torch. You will be able to see the 3 rivets at the top. I usually start pulling the panel off from the rear and work towards the door.
You'd probably be better off consulting a paintless dent remover that uses the glue system. e.g. https://www.youtube.com/watch?v=R-QmmOZjHdM