Damage player | EntityDamageByEntityEvent

Trying to use EntityDamageByEntityEvent, produces an error "does not have a handler list"
How to use EntityDamageByEntityEvent? What event uses this class or how to register a handler?

getDamager() is the function

You can only use the event in EntityDamageEvent

PHP:

public function onDamage(EntityDamageEvent $event){
if($event instanceof EntityDamageByEntityEvent){

}}

Thank you so much! Figured out