How to make enemys do damage and you dying etc

So I have a zombie arcade game in 3d, zombies can die, i do dmage, they fallow me, alls good. I Besides I need the zeds to be able to kill me as in 4 hits to me ends the game and switches to a GAME OVER scene. doesnt sound too complicated but ive been stuggling with this for the past 2 weeks. Also I would like if on each of the 4 hits blood goes on the screen and it gets redder (like in cod haha). Thanks anyone who helps! Heres my EnemyController Script:

     using UnityEngine;
     using System.Collections;
     using UnityEngine.AI;
     
     public class EnemyController : MonoBehaviour {
         NavMeshAgent nav;
         Transform player;
         Animator Controller;
     
         // Use this for initialization
         void Awake () {
             nav = GetComponent <NavMeshAgent> ();
             player = GameObject.FindGameObjectWithTag ("Player").transform;
             Controller = GetComponentInParent<Animator> ();
         }
     
         // Update is called once per frame
         void Update () {
             nav.SetDestination (player.position);
             Controller.SetFloat ("speed", Mathf.Abs (nav.velocity.x + nav.velocity.z));
         }
     }
 

HERES MY GAME MANAGMENT SCRIPT IF YOU MAY NEED IT?

     using System.Collections;
     using UnityEngine;
     
     public class GameManagment : MonoBehaviour {
         public int round = 1;
         int zombiesInRound = 10000000;
         int zombiesSpawnedInRound = 0;
         float zombieSpawnTimer = 0;
         public Transform[] zombieSpawnPoints;
         public GameObject zombieEnemy;
     
         // Use this for initialization
         void Start () {
     
         }
     
         // Update is called once per frame
         void Update () {
             if (zombiesSpawnedInRound < zombiesInRound)
             {
                 if (zombieSpawnTimer > 2.1)
                 {
                     SpawnZombie ();
                     zombieSpawnTimer = 0;
                 }
                 else
                 {
                     zombieSpawnTimer += Time.deltaTime;
                 }
             }
         }
     
         void SpawnZombie()
         {
             Vector3 randomSpawnPoint = zombieSpawnPoints [Random.Range (0, zombieSpawnPoints.Length)].position;
             Instantiate(zombieEnemy, randomSpawnPoint, Quaternion.identity);
             zombiesSpawnedInRound++;
         }
     }