How to change this to duble jump?

Hi I want to make a double jump script I made a GroundCheck so player only jump one time I made some resarch but still couldnt adding dobule jump code can u help me?,Hi I made a script and I add it GroundCheck but I dont know how can I add this double jump I resarch it but still couldnt do it can u help me?

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class PlayerController : MonoBehaviour {

 public float moveSpeed;
 public float jumpForce;

 public KeyCode left;
 public KeyCode right;
 public KeyCode jump;
 public KeyCode throwBall;

 private Rigidbody2D r2bd;

 public Transform groundCheckPoint;
 public float groundCheckRadius;
 public LayerMask whatIsGround;
 public bool isGrounded;

 private Animator anim;

 public GameObject snowBall;
 public Transform throwPoint;
 
 void Start()
 {
     r2bd = GetComponent<Rigidbody2D>();

     anim = GetComponent<Animator>();
 }

 // Update is called once per frame
 void Update()
 {

     isGrounded = Physics2D.OverlapCircle(groundCheckPoint.position, groundCheckRadius, whatIsGround);

     if(Input.GetKey(left))
     {
         r2bd.velocity = new Vector2(-moveSpeed, r2bd.velocity.y);
     } 

     else if(Input.GetKey(right))
     {
         r2bd.velocity = new Vector2(moveSpeed, r2bd.velocity.y);
     }

     else
     {
         r2bd.velocity = new Vector2(0, r2bd.velocity.y);
     }

     if(Input.GetKeyDown(jump) && isGrounded)
     {
         r2bd.velocity = new Vector2(r2bd.velocity.x, jumpForce);
     }

     if(Input.GetKeyDown(throwBall))
     {
         GameObject ballClone = (GameObject)Instantiate(snowBall, throwPoint.position, throwPoint.rotation);
         ballClone.transform.localScale = transform.localScale;
         anim.SetTrigger("Throw");
     }

     if(r2bd.velocity.x <0)
     {
         transform.localScale = new Vector3(-1,1,1);
     }
     else if(r2bd.velocity.x >0)
     {
         transform.localScale = new Vector3(1,1,1);
     }

     anim.SetFloat("Speed", Mathf.Abs(r2bd.velocity.x));
     anim.SetBool("Grounded", isGrounded);

 }

}