MainMenueResize.cs

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

public class MainMenueResize : MonoBehaviour
{
    //resize main menu elements as soon as scene is loaded
    void Awake()
    {
        /* call update functoin in Awake (Update is when scene updates,
         * and I am calling that when scene loads because only need to store
         * dynamic resolution code in one function that way and also because
         * game resolution automatically changes when I adjust device resolution
         * (at frame update). */
        Update(); 
    }

    //resize for every frame update 
    void Update()
    {
        //get first button and store it
        GameObject button = GameObject.Find("ScanButton");

        /* place button on left-centre of screen in terms of width 
         * and vertical centre in terms of height */
        button.transform.position = new Vector3((Screen.width * 0.25f), (Screen.height * 0.5f));

        //get recttransform of button so can resize it
        var buttonSize = button.GetComponent<RectTransform>();

        /* resize button to 40% of screen width horizontally and vertically
         * note: using same value for x and y because I created button image to have 
         * size 400 wide and 400 high. */
        buttonSize.sizeDelta = new Vector2(Screen.width * 0.4f, Screen.width * 0.4f);

        //get second button now
        button = GameObject.Find("ListButton");

        /* same resizing and repositioning explained for first button
         * (only difference is button is aligned right-centre instead of left centre) */
        button.transform.position = new Vector3((Screen.width * 0.75f), (Screen.height * 0.5f));
        buttonSize = button.GetComponent<RectTransform>();
        buttonSize.sizeDelta = new Vector2(Screen.width * 0.4f, Screen.width * 0.4f);
    }
}