I don't do anything. Chickens, like other birds, preen themselves. If I have a particularly dirty bird, I wash 'em with baby shampoo and blow dry. If you're having trouble keeping a frizzle in good feather, make sure you don't have a "frazzle" or "curly" bird. If a frizzle has been bred to a frizzle, you will have a frazzle which will not stay in good feather.