I only have the choice between 4 cards on the arm wrestling I don’t understand.
It’s called tavern brawl, not arm wrestling.
The decks for this brawl contain only four different cards. So when you are building your deck, you can only choose four cards.
When a match starts, you’re supposed to pick one card to remove from your opponent’s deck, and then they get ten copies each of the remaining three cards.
I don’t understand what you are asking.
Do you not understand how the brawl is supposed to work?