Place a 2 x 4, round closet rod, or similar object under the partially open lid and lean on the high edge. Better to go slowly and carefully than to go too far. The method above using a short 2×2 or 2×4 block is our preferred method and using body weight to tweak the lid towards the corners away from the hinges. It will bring it back in with a slight crest that increases sealing and appearance. They arch or banana in time from the compression seal trim (bubble trim) pressing upwards on them latched. BCB