there's not really anything you can do to finish it. in order to complete it, another player has to attack your arena team and lose to it so it's just a matter of waiting until that happens.

So does someone on my team have to die but I end up winning the match? Or is it only the matter of the other team attacking mine? I've been wondering why my team is beating the other team before they attack. Maybe I'm picking too easy of a match?

the matches you're talking about—where you pick the opponent yourself and control your team—are what are called arena offense matches. this challenge involves an arena defense match.

i

when you first started in the arena, you should have set up an arena defense team in the section circled above. the teams shown on the right that you can initiate matches with are the defense teams of other players and just as their teams show up in your arena list, your defense team will show up in the list of other players. for the challenge you're asking about to complete successfully, another player will need to find your arena defense in their list, attack it, and lose to it.

Oh, so I don't initiate the battle? Wow I had no idea. So I'll be stuck on this until someone chooses my team? That could take forever lol.

Thank you so much for clarifying!

This is sort of a "training" mission to give you a window into how defensive battles work, and how you win them. Winning on defense is usually accomplished by "tricking" the opponent with a deceptively strong team. There's lots of ways to do that, but the easier ones tend to involve using a strong champ, either with native unkillable/block damage (Skullcrown, Leorius, etc), or by using champs with Stoneskin to simulate it.