How to implement a button when the player is in the trigger

I have implemented this code and it works but i wanna make this work only if i enter the trigger and press the UI button. Right now it is changing scene automatically so, i want to press the button and then change scene. I know how to do this for PC game but not on Android game. I hope you can give me a hand.

Script

public class ButtonScript : MonoBehaviour {

    //public Button btn;
    private bool door = false;
    public bool hasCollided = false;

    public void Update () {

        if(door == true){
            SceneManager.LoadScene("InventoryScene");
            //SceneManager.LoadScene ("Scene1AToBathW");
            //Application.LoadLevel("Courtyard1F");
            //gameObject.transform.position = new Vector3(x,y,z);
        }

    }

    public void OnTriggerEnter(Collider other){
        if(other.tag == "Player"){
            //btn.gameObject.Setactive(true);
            door = true;
            hasCollided = true;
        }
    }

    public void OnTriggerExit(Collider other){
        if(other.tag == "Player"){
            //btn.gameObject.Setactive(true);
            door = false;
            hasCollided = false;
        }

    }


}