It's ideal if he steps in on his own, but you may need to place him in the tub yourself. Give him a treat if he stops trying to leave.
[header] How to wash a dog afraid of water [title] Fill a tub with a shallow layer of lukewarm water. [step] Bring the dog into the room and praise him in a gentle, encouraging tone. Place him at the edge of the tub, stroke him to help him calm down, and slowly introduce him to the water.