A pic would help... Lots of ways to repair. If there's no exposed foam, then you can just leave it. If you see foam or it's soft when poked, you'll need to leave it in the sun until any water oozes out, then at min. seal with a two part epoxy resin. Alternately, you can use some blue masking tape and shape the bottom edge and the leading edge, then take some Gorilla Glue Original mixed with a couple drops of water to fill the missing area. The glue foams up inside of your taped off form. Once dry, it easily sands to shape. Then laminate with epoxy and glass or carbon, let dry, and sand. Then spray with clear coat. You can also use Cabosil and Micro balloons as a filler. Fyi, this is a 3 day process. One day for the filler, one for lam. One for finish.

www.amazon.com/Ding-All-Epoxy-Surfboard-Repair/dp/B005JPB9DI