You can crop it, or otherwise remove information, but you can't add any. There's no underlying "perfect copy" that you can just tweak some settings and get back. (if there were, then the quality settings would be pointless because their entire purpose is to reduce the amount of data without killing your perception of the content) What you see is what you've got.
Whatever was not recorded, is lost forever. If you REALLY need it back, you'll have to re-record.