How to make the UI button (for phones) mean like on the keyboard "w" or "S"

Code:

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

public class NewBehaviourScript : MonoBehaviour
{
    [SerializeField] KeyCode KeyOne;
    [SerializeField] KeyCode KeyTwo;
    [SerializeField] Vector3 moveDirection;

    private void FixedUpdate() 
    {
        if (Input.GetKey(KeyOne))
        {
            GetComponent<Rigidbody>().velocity += moveDirection;
        }
        if (Input.GetKey(KeyTwo))
        {
            GetComponent<Rigidbody>().velocity -= moveDirection;
        }
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;

public class NewBehaviourScript : MonoBehaviour
{
    [SerializeField] KeyCode KeyOne;
    [SerializeField] KeyCode KeyTwo;
    [SerializeField] Vector3 moveDirection;

    private void FixedUpdate() 
    {
        if (Input.GetKey(KeyOne))
        {
            GetComponent<Rigidbody>().velocity += moveDirection;
        }
        if (Input.GetKey(KeyTwo))
        {
            GetComponent<Rigidbody>().velocity -= moveDirection;
        }