Character Controller with Unity User Iterface input

I have script. Then i press button that walk forward character was passed some way and stopped. So I want that when i press the ui button character walk until then I pressed the button.Function "forward"and "back" I added to ui button. This make for Android. Please help me. Unity 5

 using UnityEngine;
 using System.Collections;
 
 public class Character : MonoBehaviour 
 {
     private GameObject Player ;
     public int Speed = 5;
 
     void Start()
         {    
             Player = (GameObject)this.gameObject;
         }
 
     public void forward() 
         {
             Player.transform.position += Player.transform.forward * Speed * Time.deltaTime;
         }
 
     public void back() 
         {
             Player.transform.position -= Player.transform.forward * Speed * Time.deltaTime;
         }
 }