Looks like your clown has Lymphocystis. If so, there's not much you can do. It's a harmless virus that will come and go. Best to have pristine water conditions and fresh food mixed with vitamins like Selcon. Here's more info: https://www.reef2reef.com/threads/lymphocystis.257461/
I would recommend getting some selcon and Vita chem. Alternate adding them to your food and it should heal it self or "go away" with time.
Just for future reference API General Cure won't heal lympho. It is a virus and healthy diet with the above mentioned supplements as well as pristine water conditions are the only way to combat it.