Show him a brush, comb, towel, and nail clippers, again giving him praise and treats. You want him to anticipate only pleasant experiences with grooming and grooming tools.
Take him to the groomer for a quick trial visit. Have the groomer give a few of your dog's favorite treats to him. Let him get some adoring attention from the staff. He should have a chance sniff around for a bit, too.
Then bring him to a dog park or out for a long walk as a reward. He'll learn that going to the groomer means special time with friendly people, and fun with his favorite person afterwards.