Miller asks you to lend him a Ground-type pokémon to help expand the fields.

The Request

Talk to Miller at the Farm in Jubilife Village to accept his request.

Catch a Ground-type Pokémon

One example of a Ground-type pokémon is Geodude, which can be caught in the Deertrack Heights area of the Obsidian Fieldlands.

Lend the Pokémon

Talk to Miller to lend a Ground-type pokémon. Your pokémon will continue plowing the fields, but you can talk to Miller to switch out the pokémon with a different Ground-type one.

Reward

After you lend Miller a Ground-type pokémon, there will be more fields for farming. Talk to Colza to start a harvest.