If it's an enemy-event that has the parallel process, you should be able to add a Conditional Branch in the event-code that checks if the player has pressed the action button. The option is on the fourth tab/page The drop-down for what button to check for isn't labeled as far as "Action Button" or "Menu Button", though. It goes directional buttons, then followed by "A", "B", "C", "X", "Y", "Z", "L", "R". It's better to think of this part of the list as references to a controller than actual keyboard presses, as the "action button" on this list is "C" (by default).
Though, my guess is that you would also need to check (IE: another Conditional Branch) if the player is within attacking range (and facing the enemy-event?). However, that's a different story!