Do you mean you have red mite in your coop? Red mite don't actually live on the bird, they only come out of all the nooks and crannies at night. They feed off the bird then head back to their hiding spots. To treat red mite you need to throughly clean your coop out. Remove all perches and treat with a mite killer spray making sure you get into all the crevices. If it's quite bad with them I would treat at least twice per week and it may take a few weeks to get them under control.
If you are seeing crawling things on your birds these are more than likely lice. I treat my birds with a spot on ivermectin for pigeons. I also dust my birds with louse powder and make sure they have a dust bath so they can try and rid themselves of the lice.