1) Create a separate hit box sprite for the bat - literally just a square. This will be used to detect collision with an enemy
On the attack animation frames, decide where you want the collision to actually take place and create an additional image point (this is where we will spawn the hitbox)
In your event sheet:
Player, Attack animation is playing.
Player, Attack animation frame = <whichever frame you want the hit box to appear> --- Create hit box at image point (xyz)
Player, Attack animation on ended - destroy hit box
Hit box on collision with enemy - destroy enemy (or subtract a value from enemy hp, if you want the enemy to take more than 1 hit to kill)