Depends on the game

Tactic 1: Win once, then refuse a rematch. No one said you have to keep fighting them just because they won't stay down.

Tactic 2: Don't fight them; sneak past them. They can't reset if they can't find you.

Tactic 3: Convince them to join your party. Clearly they are an invaluable asset.

Tactic 4: Hack into the code and disable resets. Of course, if you lose that won't be pretty...

Tactic 5: Beat them again and again and again until they rage quit. Even if it's an AI, it has to give up some time.

Tactic 6: Turn them to stone or trap them.

Tactic 7: Run away screaming IRL because clearly there is something NOT RIGHT about this game.