Maris asks you to make a Bean Cake for the hungry Piplup who won't eat.
The Request
Go to the southeast area of Cobalt Mirelands and approach Maris to accept the request.
Give Maris a Bean Cake
After you get a Bean Cake, make sure it is in your Satchel, then give it to Maris.
Reward
You will get 5 Razz Berries and 3 Hyper Potions as a reward.