Scoop joint compound onto a drywall taping knife. Apply a thin layer of compound onto the recessed area of the wall, using the taping knife.
Wait 24 hours to allow the patch of freshly applied joint compound to fully dry. Put on a dust mask, eye protection and a hat, such as a baseball cap. Fold 120-grit sandpaper over in half, and lightly sand down all raised ridges across the entire patch. Sand with the paper flat against the wall, to avoid making angles. The mask, eye protection and hat protect you from the white dust particles that result from your sanding.
Scoop up and apply a second layer of joint compound onto the patch, using the taping knife. Feather the compound out a little farther than the edges of the first patch. Allow the fresh layer 24 hours to dry.
Put on the dust mask, eye protection and hat, and lightly sand down all the rough spots and ridges across the patch, using 120-grit sandpaper.
Apply any additional coats that are needed to bring the recessed spot on the wall level with the rest of the wall. Allow each successive coat 24 hours to dry, and sand the coat smooth, using the sandpaper.