Your car's rear bumper probably is the area most likely to get bumped or dented at some point. Most bumpers on cars made today are plastic and can be repaired using one of several methods.
Repairing with Heat
If the bumper is dented but has no chipped paint, repair it using heat. Remove the bumper from the vehicle. Look under the edge of the bumper and locate the black plastic circles. There is a place in the centre of each circle for a screwdriver. These are plastic clips holding the bumper in place. Use a screwdriver to press into the centre of the clips and turn. When the centres come out, remove the outer ring of the circle with your hand. Next, remove the screws along the edge located inside the wheel wells, close to the tires. Look along the top edge of the outside of the bumper for any additional screws. Remove them and remove the bumper.
Locate the backside of the dent. Use a heat gun or blow dryer to heat the inside of the dent. It may take between five and ten minutes to fully heat the area. Wearing thick gloves, gently press on the area until the dent is pushed out. Replace the bumper and all hardware.
If the dent can't be pushed out with heat, fill it with body filler. This method is best applied while the bumper is still on the car. Use a lightweight material sometimes called putty. (Don't use hard filler, like Bondo.)
Grind the dented area carefully so that only the paint is removed. Pressing too hard can gouge the bumper.
Once the paint is removed, spread a thick layer of putty in and over the dent. Allow the putty to dry for at least an hour, depending upon the thickness. Sand the putty smooth using 120-grit sandpaper. Sand until the putty is even with the surrounding area.
Once the repairs have been made, spray a thin coat of automotive primer on the areas that have been sanded. Allow the primer to dry for 30 minutes. Spray three to four coats of paint over the primer, allowing each coat 30 minutes to dry. Spray two or three coats of clear coat paint over the dried paint. Allow the paint a full day to dry.