How to change arrow(s) damage

Ok so i want too know how do u change a/an arrow(s) damage?

entitydamageevent and check the cause. If it is a arrow then setcancelled then give the hurter damage your self.

so

Code:

if($cause === EntityDamageByArrowEvent)?

No.

PHP:

public function onHitByArrow(EntityDamageEvent $event){
    if($event->getCause() === 2){
        $event->setCancelled(true);
        $event->getEntity()->attack(WHAT EVER HERE);
    }
}

PHP:

If($event instanceof EntityDamageByChildEntityEvent and $event->getChild() instanceof Arrow) {
  $event->setDamage($new_damage);
}

i did something like this and it worked