How I make a damage to the player without using a colliderEnter2D?

I am doing a 2D videogame and the enemy throw a bullet, when it finished his animation, it makes a damage to the player and it is represented in the life bar. But I have a problem between the EnemyBullet script and HealthPlayer script, because the player do not receive damage and the life bar do not change. Could anybody help me, please?

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class PlayerHealth : MonoBehaviour
 {
 
     public int life;
     public GameObject lifeUI;
 
 
     // Use this for initialization
     void Start()
     {
 
     }
 
 
     void Update()
     {
 
     }
 
     public void getDamage(float damage)
     {
         life -= (int)damage;
         if (life >= 0)
         {
             life--;
             lifeUI.GetComponent<Image>().fillAmount -= 0.1f;
         }
     }
 }

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class EnemyBullet : MonoBehaviour {
 
     public GameObject obj;
 
     private PlayerHealth player;
     private float damage = 1f;
     private float timeToKill = 2f;
     private float initTime;
 
     public void Start() {
         player = obj.GetComponent<PlayerHealth>();
         initTime = Time.time;
     }
 
     private void Update() {
         if(Time.time >= initTime + timeToKill) { 
             Destroy(gameObject);
             player.getDamage(damage);
         }
     }
 
     private void OnTriggerEnter2D(Collider2D collision) {
         Debug.Log("Shot");
         Destroy(gameObject);
     }
 }