Open the back door, remove the decorative panel at the back, and knock the felt from the inside out with a hammer. After the dent is knocked out, use a grinder to grind off the paint where it needs to be repaired, and then use a bull's head planer to completely pull it out and level it. Finally, blow the putty, and start painting after blowing the putty. Finally, put on the back door decorative panel, and it is finished.