(C#) Follow target (script) transform target PREFAB

Hi everyone! I want to use the script "follow target" with a prefab but I don't arrive to select my prefab. Why?

The script:

using System; using UnityEngine;

namespace UnityStandardAssets.Utility { public class FollowTarget : MonoBehaviour { public Transform target; public Vector3 offset = new Vector3(0f, 7.5f, 0f);

     private void LateUpdate()
     {
         transform.position = target.position + offset;
     }
 }

}