It looks like Hole-in-the-Head disease. On bettas I believe it presents as pin-sized holes like that...usually caused by unclean water conditions, underfiltration, etc.
I'm not sure if you can cure this disease. From what little I know, it's one you can only hope to stop before it progresses further. Hopefully someone else will have a medication to recommend. I've never had to treat this myself.
I'm aware it's been a while but I found this by a recent search, so I wanted to leave this information here for others that may also find this in recent time and times to come.
This is not HITH-these are sensory pits that are perfectly natural and that a betta should have. We just are not used to seeing them so prominent, as most people are used to darker color betta or just don't look that closely to their betta's head.