Kochika asks you to deal with the enraged pokémon in Oreburrow Tunnel.

The Request

Talk to Kochika in Galaxy Hall in Jubilife Village to accept this request.

Go to Oreburrow Tunnel

Go to the Obsidian Fieldlands, and go to the guidance marker east of Heights Camp. Approach the Alpha Onix and there will be a cutscene. Approach the Alpha Onix again and you will battle it. You aren't allowed to try to catch it, so just focus on defeating it.

Reward

You will get 20 Iron Chunks and a Grit Rock.