If your rabbit is still alert and not too lethargic, then your rabbit should be fine if you take some steps to help bring his temp down. If he is very lethargic, unresponsive, and/or mouth breathing, you will need to get him to a vet immediately.
The wetness around the mouth could be from drinking, or from drooling which can happen from heat stress. You need to get him cooled down. Bring him into a cool area(preferably with AC). Provide a water dish with cool water in it, wetting the ears with a cold washcloth, turn on a fan but don't have it blowing directly on your rabbit, place a frozen water bottle next to your rabbit(or a baggie with ice cubes), and if you have a cement floor or cool tiles let your rabbit lay on that.