Change Sprite Image in Runtime

Good day, I'm having a problem here, No error so far but I can't seem to display my desired Sprite Image in my Resources directory.

here's my code

 public void Spawner(){
 
         int platformRange = Random.Range(3,5);
         float nextPlat = 0f;
         float randomDistance = Random.Range(-2f,1f);
         float nextPlatY = Random.Range(-5f,-.5f);
         float nextTotalPlatWidth = 0f;
         for (int i =0; i <= platformRange; i++) {
             
             GameObject platform;
             SpriteRenderer rend = platform.GetComponent<SpriteRenderer>();
             Debug.Log (platformRange);
             if (i == 0) {
                 platform = plat [0];
                 platformLocation = "LeftPlat";
                 platformStyle = "leftedge_";
             } else if (i == platformRange){
                 platform = plat [2];
                 platformLocation = "RightPlat";
                 platformStyle = "rightedge_";
             }
             else{
                 platform = plat [1];
                 platformLocation = "MiddlePlat";
                 platformStyle = "middlesection_";
             }
     
 
             rend.sprite = Resources.Load (platformLocation + "/"+ platformStyle + itemName) as Sprite;
 
 
             Debug.Log ("POSITION" + transform.position.x + totalPlatWidth + nextPlat + randomDistance);
             Vector3 spawnPosition = new Vector3 (transform.position.x + totalPlatWidth + nextPlat + randomDistance, nextPlatY, 0f);
             nextPlat = nextPlat + platform.GetComponent<Renderer> ().bounds.extents.x * 2 - .1f;
             if (i == 0){
                 Instantiate(SpawnerObj,new Vector3(spawnPosition.x,-0.0400f,0f),Quaternion.identity);
 
             }
             Instantiate (platform, spawnPosition, Quaternion.identity);
 
         }
 
     }

Function Spawner is triggered by a collision.