Here you go,
this is the script for the bullet.
func _on_bulletarea_body_entered(body):
if body.is_in_group("enemy"):
body.queue_free ()
queue_free()
attach an area 2d to the bullet , Connect the signal of the area2d to the bullet script (body_entered)
and add your enemy to the group enemy (add_to_group("enemy"))
it should work perfectly fine