Unfortunately, once the
nail turns black it will be lost and the
nail will have to regrow.
The drill is, if a fingernail or toenail is bruised, to permit the blood to drain immediately. This is a painless, but somewhat squeamish procedure. Take a long-nosed needle nose pliers and heat a safety pin in a flame. Then burn a tiny hole in the part of the nail directly above the bruised part. Stop when blood oozes out. This will be painless. There are no pain sensors in the fingernail or toenail.