unity – Replace Space bar by UI button to jump

There is a jump script and it works correctly on my pc.
How can I use UI button instead of Space bar?

there is three input in my code

Input.GetKeyDown(KeyCode.Space)

Input.GetKey(KeyCode.Space)

Input.GetKeyUp(KeyCode.Space)

and I just want to replace Space bar to UI button, please somebody help me <3.

    private Rigidbody rb; 
    public float jumpForce;        
    private bool isGrounded;        
    public Transform feetPos;       
    public float circleRadius;      
    public LayerMask whatIsGround;  
    public float jumpTime;          
    private float jumpTimeCounter; 
    private bool isJumping;       

    void Start ()
    {
        rb = GetComponent<Rigidbody>();  
    }

    private void Update()
    {
        isGrounded = Physics.CheckSphere(feetPos.position, circleRadius, whatIsGround);

        if (isGrounded == true && Input.GetKeyDown(KeyCode.Space))  
        {
            isJumping = true;                    
            jumpTimeCounter = jumpTime;                
            rb.velocity = Vector2.up * jumpForce;       
        }

        if (Input.GetKey(KeyCode.Space) && isJumping == true)
        {
            if (jumpTimeCounter > 0)                    
            {
                rb.velocity = Vector2.up * jumpForce;   
                jumpTimeCounter -= Time.deltaTime;      
            }
            else                                        
            {
                isJumping = false;                     
            }
        }

        if (Input.GetKeyUp(KeyCode.Space))              
        {
           isJumping = false;                          
        }
    }