If you can give the fish with the damaged fins its own tank, that is sometimes the best situation. If not, then you want to avoid keeping them with other mature angelfish. Adult angelfish have a strong territorial instinct and will harass new fish, so moving it into another tank of mature angelfish will seldom work.
What I have been doing for years, is to move the injured fish into a tank of juveniles. In such a situation, the stressed adult, will completely ignore the juveniles and the juveniles have no desire to harass a large fish. The small fish also have not yet developed territorial guarding unless there are not many in the tank. I always choose a tank that has a good number of juveniles in the tank. I've used this techniques hundreds of times and it has yet to fail.
Make sure to not overfeed the juveniles and to change a lot of water each day. Water quality has to be high if you want the injured fins to regrow. Here is an example of a recent damaged adult female albino dantum. Her caudal was chewed off in the area surrounded by the red line in the main photo. She was found in the back of a tank where a pair had formed and she wasn't moving. This video is after two weeks with a group of quarter sized black juveniles. She has recovered and the fins have regrown completely, though the fin pattern is now gone from the portion that was chewed off.
If you can't do any of this, then a tank-divider will be necessary to isolate the injured fish. If you are proactive early on, the fins will likely heal with a lower chance of bends or kinks. If you delay, then the fin may regrow with flaws.