Well, the only thing that’s left is to attach an box collision component to your character; scale it to your needs; bind your enemies to a single, specific class; and write the code that says “every time that I press this button, any actor of this class takes ‘X’ damage if they are inside this collision component.”
You would have to run a boolean to see if an actor of the enemy class is inside the box, first. After that, you would have to find a way to only inflict the damage on whatever’s inside the box.
But it might be easier to skip the class part if you aren’t worried about friendly fire.