pocketmine\entity\Entity::extinguish PHP Method

    public function extinguish()
    {
        $this->fireTicks = 0;
        $this->setDataFlag(self::DATA_FLAGS, self::DATA_FLAG_ONFIRE, false);
    }

 public function onEntityCollide(Entity $entity)
 {
     $entity->resetFallDistance();
     if ($entity->fireTicks > 0) {
         $entity->extinguish();
     }
     $entity->resetFallDistance();
 }