1) Tape or sticker
You can sticker or tape the area as a temporary fix. If there is no actual breach in the hull, this might be the best option here, as you can always take your repair further if needed.
2) Paste Epoxy or sealant
Marine centers will have past compound kits that you can rub into dings, these work in water as well. When doing a long voyage I carry some with me.
3) Epoxy Resin
This will take more time then the other options above, but will be closer to a complete repair. I suggest SolarRez, a UV activated epoxy resin. You can purchase on Amazon, marine center or surf shop should all have or similar.