You want to get the shower water just barely warm first, then aim the shower head at the wall, so that the water bounces off the wall, and only a small amount hits the chameleon, which should then be placed on a perch (preferably a plant) in the shower.
The chameleon should be allowed to "enjoy" this for up to 45min.
Check water temp periodically to make sure it is warm, but not hot or cold.
Make sure no water is pooling up if at all possible, to avoid any drowning accidents.
You should then make changes to your husbandry to correct the issue.
When doing the shower be sure the water is between 75-80 degrees . Longer mistings and a dripper should help your chameleon from becoming dehydrated.if
A couple tips on the dripper.
*make sure to use lukewarm water. (not to hot/cold) Sometimes water can be too cold for them and then they stay away from the drippers.
*Have it so the dripper is dripping onto leaves or a vine. Give it a "running" affect.
*Let it run for a couple hours.