Are the mites gone since you treated with the Elector PSP?
If not, use Permethrin Poultry Dust. Put the dust in a sock, then tap the sock all over him like a powder puff, this will give you a fine layer of dust to work down through the feathers to the skin. Dust him all over.
Mites will suck the life out of a chicken, if he's unable to stand or walk, he's in terrible shape and is not able to take a dust bath.
IF the cause of his inability to walk a or stand is cause by mites only, do whatever is needed to eliminate the mites. Work on getting him drinking, feed him an 18-22% protein chick starter or all flock feed, give some beef liver a couple of times a week or some egg. It would be a good idea to also get some poultry vitamins into him.
Photos of the rooster and housing may be helpful. Mites also live in housing, so that needs to be treated too.