How can I reuse an variable that has been instanciated

Hello i'm a begginer in Unity and I have a little problem. I want to reuse for exemple, the variable "issou" in the start() , but I can't because it's a local variable. But how can i do for exemple if I want to change the variable position or something ?

Thank You.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class GenerationTerrain : MonoBehaviour {
 
     public GameObject cube;
 
     // Use this for initialization
     void Start () {
 
         // instanciation de trois morceaux de terrain
 
         var issou = Instantiate(cube, transform.position = new Vector3(1,2,3), transform.rotation);
         issou.transform.localScale = new Vector3(10000, 100, 1000);
         issou.GetComponent<Renderer>().material.color = Color.red;
 
         var issou2 = Instantiate(cube, transform.position = new Vector3(1000, 2, 3000), transform.rotation);
         issou2.transform.localScale = new Vector3(10000, 100, 1000);
         issou2.GetComponent<Renderer>().material.color = Color.green;
 
         var issou3 = Instantiate(cube, transform.position = new Vector3(2000, 2, 6000), transform.rotation);
         issou3.transform.localScale = new Vector3(10000, 100, 1000);
         issou3.GetComponent<Renderer>().material.color = Color.blue;
 
 
     }
 
 
     // Update is called once per frame
     void Update () {
 
     }
 }