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.
https://www.amazon.com/
https://www.amazon.com/Clear-
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.
https://www.amazon.com/3M-
https://www.amazon.com/WEST-
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.