GetAxis to GetTouch

hello everybody... im new and i start learn unity with their lessons !!! On first project of unity, Roll a Ball, it give me a this code:

 using UnityEngine;
 using System.Collections;
 
 public class PlayerController : MonoBehaviour {
 
     public float speed;
 
     private Rigidbody rb;
 
     void Start ()
     {
         rb = GetComponent<Rigidbody>();
     }
 
     void FixedUpdate ()
     {
         float moveHorizontal = Input.GetAxis ("Horizontal");
         float moveVertical = Input.GetAxis ("Vertical");
 
         Vector3 movement = new Vector3 (moveHorizontal, 0.0f, moveVertical);
 
         rb.AddForce (movement * speed);
     }
 }

If i replace Input.GetAxis with Input.GetTouch their not work... how i can fix the code for try the project on my device Android and continue the lessons of unity? I prefeer modify the code, because i understand it with unity lessons... thanks so much to all!