Once you get there, talk to Zumi and she will tell you something about the wagon that she built. The problem is that it’s missing one wheel as well as a horse that can pull it.
With that said, your first objective is to repair the wagon. Head to the back of the stable and grab two of the wagon wheels lying on the ground.
Head back to the wagon and attach the wheels to their respective spots. Once the wagon is finished, your next task will be to catch a wild horse.
Go to the field and look for a wild horse nearby. Once you find a horse, approach it and attempt to mount it. Keep in mind that it will also attempt to kick you if you get too close.
You can crouch as you approach a wild horse that you want to tame. This way, they won’t be able to run away since they won’t notice you unless you start mounting one of them.
With a wild horse captured, get back to the stable and talk to Zumi. Choose “All yours!” from the dialog options afterward.
After a few lines of dialog, the quest will then be completed. You’ll then be rewarded 100 Silver Rupees for all your troubles.