Hello and welcome to FF Marissa! From pic it appears a small wound that might have gotten infected. I would place frog in a hospital like enclosure. That is just a small enclosure with damp paper towels (use dechlorinated tap) as substrate, a daily changed water dish, and some artificial plans to reduce stress. Get some plain Neosporin (without pain killer) at drugstore and apply to wound couple times daily. If you take frog to veterinary can get stronger antibiotic and pro opinion too. Here is a nice care article for them: Frog Forum - Fire-Bellied Toad Care and Breeding - Bombina orientalis and relatives. Good luck !