A dent after an injection can come from fat loss, scar tethering under the skin, or a combination of both. The right treatment depends on whether the area is simply hollow, stuck down to deeper tissue, or has any remaining firmness from the old injection. Common options include scar release or subcision, fat grafting to restore volume, and sometimes injectable filler or biostimulator in carefully selected cases. If the depression is tethered, adding volume alone may not fully correct it unless the scar bands are released first. I would recommend an in-person consultation with a board-certified plastic surgeon who can examine the area while standing and moving, since it is visible through clothing. If there is any concern about old foreign material or a firm mass, ultrasound or MRI may be useful before planning treatment.