HITH literally looks like holes appearing in the head. It starts out as indentations.
What you're seeing is an inury, like others said, possibly with some fungus growing on the exposed surface.
It will heal itself as long as you keep the water clean. Water changes are helpful with healing injuries by keeping pollutants and bacteria under control.
Just watch for secondary infections. If it starts to look worse or spread, only then do you need to look into meds. Just like a wound on yourself, it will usually heal on its own if kept clean.