Hi ashmunkie and welcome to the forum. How has your betta been acting? Is he eating and swimming normally? It does look like that is a cyst but it's also possible he has a fluke dug into his fin. If you don't have live plants in your tank, then I'd suggest starting a treatment of aquarium salt for now. The dosage is one tsp per gallon; take a bit of tank water and let the salt dissolve in a separate cup before pouring it in. Change the water every day for five days and redo the salt treatment. If he's not any better, up the salt dosage to 2 tsps per gallon and continue for another five days. If he's still not better or has gotten worse at any time, he may need medications.
OR, if you want to make it easier for the daily 100% water changes or you have live plants in your tank, you can do th salt treatment in a small QT container like a cup or bowl. Put half of his tank water in the container. In a separate large jug, mix up a gallon of dechlorinated water and one tsp of salt. Let the salt dissolve then fill the rest of the container with the water; save the rest of the salt water for future water changes.
I hope this helps. Keep us posted!