I need help what do I do this is a adult Iguana and has been doing this for a few days now

Is it possible he's shedding? Check the spikes along the ridge of the tail and see if he has any retained shed on them. Also look for reptile mites. They are small parasitic arachnids that will suck the blood of reptiles (similar to fleas and ticks). They are small, usually less than a millimeter in length, and are usually black (the common snake mite) or red ("chigger" mites). They're a pain to get rid of.