If the indented scar is fairly shallow, then dermabrasion or an ablative laser treatment might reduce the edges of the crater to produce less shadowing. Attempting to fill the area with collagen
or a hyaluronic acid filler
(Restylane or Juvederm) might help a little, but would require repeated injections. To completely eliminate the depression, assuming the scar is small enough, then complete surgical resection of the depressed area would be appropriate.