Can't Get Prefab Clone To Follow Mouse

I already looked up questions for the following question, however I am still not getting the results I need. I created the Prefab called "Ground". I then made a script called "PrefabCreation".

Prefab Creation:

 using UnityEngine;
 using System.Collections;
 
 public class AssetCreation : MonoBehaviour {
 
     public GameObject target;
 
     Vector3 mousePos;
 
     void Start(){
     }
 
     void Update(){
         mousePos = Input.mousePosition;
         mousePos.z = 10f;
 
         target.transform.position = Camera.main.ScreenToWorldPoint(mousePos);
     }
 }

In order for the Prefab to follow the mouse I need to drag the selected Prefab into the scene, then use the created Prefab's transform as the reference. It works, but not what I needed.

When creating an instance/clone of the Prefab into the game during run time when a key is pressed, I use this code:

 Transform groundT = (Transform)Instantiate (target, transform.position, transform.rotation);

However, I can't get that current clone to follow the mouse. The code above is in an Update function. I am using C#.