Tinnie in Beach Field 3 is looking for her volleyball. Lifeguard Bean in Blooming Cora has it. He can be a bit tricky to find if you aren't familiar with Blooming Cora. Walk to the bottom right of the town and you will find him up a tree.
He will give you a gift box to take to Tinnie. If you already have the box when you talk to her the first time be sure to talk to her again and get your reward.
