After meeting both prerequisites, go to the Pumpkin Landing and speak with Kina in the pumpkin field. She’ll ask if you can get someone to help her plow the field for her. Tell her that you do.
Fly on over to Eldin Volcano, landing at the “Volcano East” Bird Statue. Go north some, using the air spurts to reach the ledge, then run and sky-dive into the cave below.
Land on the ledge with the Mogma (towards the north). Speak with him and he’ll agree to plow the field. Scrapper comes to carry him. Go back to a Bird Statue and start flying back to Pumpkin Landing. Speak with Kina for your reward.