I don't think there is much to do with a cyst. My betta has a bump too! Near his eye. In my case I think his scales have grown funny, I'm hoping it will pop off or stay the same and not cause any issues.
Just keep him happy and healthy in good living conditions with good food and you should be good!
If it pops off it may leave an open sore in which case you may want to do a bacterial treatment or something just to prevent infection. But don't worry about that unless it happens! He will just have a beauty mark like mine for now!
Best of luck!