How to duel Many Falling Rocks [Tin Star]?

I think I once accidentally found the right combination of choices that would have let me duel him one on one, but my Brawl stat in that specific walkthrough was low so I didn’t choose to fight him. When I restarted it and boosted my Brawl stat I couldn’t remember how to duel him and ended up making peace instead.

I’d really like to know how to duel him, if anyone knows?