I am afraid you are not going to get much help from the doctors. If you even suggest his condition is related to the vax, it will be dismissed. So, unless you have a special provider that is not on board with the narrative, do not expect too much. Providers are seeing some weird stuff. Unfortunately, most are not relating it to the jab.

They might right a script for steroids. It depends on the rash. There are different causes for rashes - most are allergic in nature. But if we are dealing with a vax adverse reaction, all the normal rules are out the window. It could also be latent viral reactivation like with shingles. The jab has also been linked to some autoimmune reactions with the skin and those can be nasty. It could also be vascular as in vasculitis. The main thing is make sure they run a d-dimer test to check for clotting. Let's just hope he has something simple that can be easily treated and not linked to the vax. But if not, it may be much harder to get a diagnosis much less be treated. Some of the more complicated conditions really don't have curative treatments like with autoimmune diseases. Good luck.