Enemy walking above ground

Hi there!

So my problem is that my enemy which is a zombie is walking above the ground when he wants to chase me.. here's my script for my enemy :

 var target : Transform; //the enemy's target
 var moveSpeed = 3; //move speed
 var rotationSpeed = 3; //speed of turning
 
 var myTransform : Transform; //current transform data of this enemy
 var isNotDead : boolean = true;
 var health : float = 100;
 function Awake()
 {
     myTransform = transform; //cache transform data for easy access/preformance
 }
 
 function Start()
 {
      target = GameObject.FindWithTag("Player").transform; //target the player
 
 }
 
 function Update () {
     
     if(health < 1){
     
         isNotDead = false;
         animation.Play("die");
         Destroy(gameObject, 1);
     }
     
     if(isNotDead){
     
         //rotate to look at the player
         myTransform.rotation = Quaternion.Slerp(myTransform.rotation,
         Quaternion.LookRotation(target.position - myTransform.position), rotationSpeed*Time.deltaTime);
     
     
         
         var distance = Vector3.Distance(target.position, myTransform.position);
         if (distance < 3.0f) {
             animation.Play("attack1");
         }
         else{   
             //move towards the player
                myTransform.position += myTransform.forward * moveSpeed * Time.deltaTime;
                animation.Play("walk1");
         }
 
     }
 }
 
 function ApplyDamage(dmg : float){
 
     health -= dmg;
 audio.Play();
 }

anyway there are bunch of animations set up to this enemy and i have freezed the x,y,z in the Rigidbody ( freeze position ) Please help me ASAP! Thanksss