Make sure they have access to shade and fresh water, and supplement electrolytes as well as allowing access to free choice salt. Don't put on fly sheets or any sort of a covering and if you use fly spray with mineral oil, switch to one with a water base. If they have a run in, you could try hanging a box fan if that's at all feasible for you.
Hey! You can try to clip him in the areas where he sweats more or the whole body if it's necessary!
Hope it helps