Lower the stress as much as possible. Turn out the lights. And really boost the O2 levels as possible.
I hesitate to suggest but a bath in Ruby Reef Rally works wonders on fish in rough condition. It's combination of antibiotic and antiseptic qualities often produces results.
Another med I suggest for fish with "red sores" in Nitrofuracine Green Powder. Lots of suppliers and LFS treat roughed up, starved, newly received fish with this powder. Very good results.
Here's a thread by Humblefish that may help with some insight into really sick fish:
https://www.reef2reef.com/threads/alprazos-salvage-protocol.213599/