How do you fix a dented door?

If its a nice big wide dent you may be able to pop it out take off the door panel make sure the window is up use a small block of wood to pop it out

if its a small dent then you need a grinder pondo primer paint sander etc a lot of time an patience

When a dent occurs, the metal is pushed in. The force that pushed in the metal also pushes some areas around the dent out. These are ridges or crowns that must first be pushed down to relieve the pressure and allow the dent to be pushed out from behind, or if large and soft enough pulled out with a suction cup. Paintless dent removal is the art of removing dents without the use of paint and bondo. Paintless dent removal technicians use tools to push the dent out from the back side of the dent. You can find paintless dent removal technicians in your area by searching for paintless dent removal on google in your area. PDR Paintless dent removal technician can remove most dents at a lower cost than most conventional body shop repairs.