How to create a button in unity from Input.GetMouseButtonDown

Question

How can I create a touch event or UI button that can execute the code below. I got that code from an asset that meant for PC i want to re-create that project for android mobile

using UnityEngine;

using System.Collections;

public class PlayerIO : MonoBehaviour {

RaycastHit hit;
int maxBuildDist = 10;
public Transform RetAdd;
public Transform RetDelete;
public Transform Player;
public GameObject Player_Camera;
Color Block_Color = Color.blue;
bool Block_Menu = false;

void Start(){
    RetAdd = GameObject.Find("RetAdd").transform;
    RetDelete = GameObject.Find("RetDel").transform;
    Player = GameObject.FindGameObjectWithTag("Player").transform;
    Player_Camera = GameObject.Find("Main Camera");
}

void Update(){
    if(Input.GetKeyDown(KeyCode.E))
        Block_Menu = !Block_Menu;
    if(Block_Menu){
        Time.timeScale = 0;
        Player.GetComponent<MouseLook>().enabled = false;
        Player_Camera.GetComponent<MouseLook>().enabled = false;
        //((MonoBehaviour)Player.GetComponent<FPSInputController>()).enabled = false;
    }
    if(!Block_Menu){
        Time.timeScale = 1;
        Player.GetComponent<MouseLook>().enabled = true;
        Player_Camera.GetComponent<MouseLook>().enabled = true;
        //((MonoBehaviour)Player.GetComponent<FPSInputController>()).enabled = true;
    }

    if(!Block_Menu){
        if(Physics.Raycast(Camera.main.ScreenPointToRay(new Vector3((Screen.width / 2), (Screen.height / 2), 0)), out hit, maxBuildDist)){
            RetAdd.GetComponent<Renderer>().enabled = true;
            if(hit.transform.tag == "Block"){
                RetAdd.transform.position = hit.transform.position + hit.normal;
                RetDelete.transform.position = hit.transform.position;
                RetDelete.GetComponent<Renderer>().enabled = true;
            }
            if(hit.transform.tag != "Block"){
                RetDelete.GetComponent<Renderer>().enabled = false;
                RetAdd.transform.position = new Vector3(hit.point.x, hit.point.y + 0.5f, hit.point.z);
            }
            if(Input.GetMouseButtonDown(0)){
                GameObject block = (GameObject)Instantiate(Resources.Load("Block01"), RetAdd.transform.position, Quaternion.identity);
                block.GetComponent<Renderer>().material.color = Block_Color;
            }
            else if(Input.GetMouseButtonDown(1) && hit.transform.tag != "Floor"){
                Destroy(hit.transform.gameObject);
            }
        }
        else{
            RetAdd.GetComponent<Renderer>().enabled = false;
            RetDelete.GetComponent<Renderer>().enabled = false;
        }
    }
}

void OnGUI(){
    if(Block_Menu)
        Block_Menu_GUI();
}

void Block_Menu_GUI(){
    GUILayout.BeginVertical();
    if(GUILayout.Button("Green"))
        Block_Color = Color.green;
    if(GUILayout.Button("Red"))
        Block_Color = Color.red;
    if(GUILayout.Button("Blue"))
        Block_Color = Color.blue;
    GUILayout.EndVertical();
}

}

this is the whole code of the script that I want to change. I already had a joystick control but the problem is since I'm using that OnMouseDown whenever I click my joystick the object is spawning