3-star to 5-star Friendship Caf? (Moon Exclusive) and Friendship Parlor (Sun Exclusive) sell EV reset services. They sell a single EV reset service for one specific stat at the 3-Star Ranking, and get a new EV reset service for another stat at each star after; up to three EV reset services at a 5 star ranking. Friendship Caf? can reset your Sp. Atk, Sp. Def, and Speed EVs. Friendship Parlor will reset your HP, Attack, and Defense EVs. They are both version exclusive, and the only way to get both in the same game is to have one of your Festival Plaza visitors recommend it to you from the other game (but from my experience I only get 1 star stores).
There are also 6 different types of berries. Pomeg, Kelpsy, Qualot, Hondew, Grepa, and Tamato berries reduce the EVs of one specific stat by 10 EVs each. The berry tree on Route 10 gives three random berries of any combination, and you can pick new ones each day (save before the tree and reset if you need specific berries). You can grow more of these in Pok? Pelago on Isle Aplenny, and you get anywhere from 5-14 of these specific berries after harvest. You are guaranteed to get the max amount I believe, if you have the highest upgrade for Isle Aplenny and you use Pok? Beans to make them grow faster. They take 48 hours to grow but adding in enough Pok? Beans will make them grow twice as fast. A combination of mainly Plain Beans and a few Patterned Beans is enough to make the bean effects last for 24 hours so that you can harvest your berries exactly a day after you plant them.