Wash the door well with a mixture of a gallon of hot water and a quarter of dishwasher detergent.
Then, rinse the area well and let it dry completely. A hair dryer will help speed up the process.
Sand the dented area with some eighty grit sandpaper. This will rough up the surface and help the patching compound to grab onto the dented area. Wipe away any sanding dust.
Use a plastic putty knife to fill the dent with patching compound that is suitable for metal. Smooth the patch, feathering it out around the repair just like you would if you were patching drywall. Then let it dry completely.
Once it has dried, use some one hundred twenty grit sandpaper to smooth the patch even with the surrounding door.
If the dent is deep, you may need to add a second coat of patching compound.
Now that I've primed and painted, the door locks look like new! I'm Mrs. Fixit and it's just that simple!