When your character performs a attack action spawn an "punch" sprite in front of your character, then in your events have an event for the collision of that sprite with the enemy for damaging the enemy. Destroy the "punch" sprite destroy after collision with an enemy or after a very short time ( the fade behaviour is good for this - fade in: 0, wait: 0, fade out: 0.1, destroy: true ). You can either have the sprite be transparent or set the initial visibility to false so that it doesn't appear.
There's a few other cool things you can do with this as well, it's kinda handy.