Give your chameleon a bath or shower as needed. Usually not sooner than once a week. This helps hydrate and circulate your chameleon internally. The steam and humidity also helps his respiratory system.
In the shower place a plant in the stall and let your chameleon sit on it. Allow the warm shower to touch him indirectly.
Or, you can fill a plastic tub with enough warm water up the the chameleon's armpits and allow him to be in it about 20 minutes.
If you do this on a warm day outdoors be sure to stay with your chameleon and put a protective screen above the tub so a bird, cat, dog, etc., cannot harm your chameleon.