Flame angel has fin rot or fin infection

Hello everyone. Im new to the hobby and just recently added a flame angelfish to a 72 gal tank. My tank has blue devil demsel, three clownfish, one yellow tang, and one blue regal. The flame angel was introduced last a week ago. At first i didnt see any problem until i noticed the right pectorial fin stop flapping with no visual sign of damage. I didnt really care until it started swollen up at the base and turning white. The tail fin was also ripped so i started to psopay attention and noticed it was the blue devil demsel that has been picking on the flame angel. I tried to catch the damsel but he is too fast and always hide behind the rocks. The aggression seems to be less and less as time goes by. My question is will the flame angel recover from the injuries or do i need to treat it with any type of medication? Both fish are almost impossible to catch unless i remove the rocks. Your help is greatly appreciated.