Singleton HELP

I need to implement these codes in singleton but I have no idea about how to do it. I am new at coding Anyone can help? Or show to the way how to do it ?

Thanks!

using GooglePlayGames;
using GooglePlayGames.BasicApi;
using UnityEngine;

public class GooglePlayGameScript : MonoBehaviour {

// Use this for initialization
void Start () {
	PlayGamesClientConfiguration config = new PlayGamesClientConfiguration.Builder().Build();
	PlayGamesPlatform.InitializeInstance(config);
	PlayGamesPlatform.Activate();

	SignIn();
}

void SignIn()
{
	Social.localUser.Authenticate(success => { });
}


#region Leaderboards
public static void AddScoreToLeaderboard(string leaderboardId, long score)
{
	Social.ReportScore(score, leaderboardId, success => { });
}

public static void ShowLeaderboardsUI()
{
	Social.ShowLeaderboardUI();
}
#endregion /Leaderboards

using UnityEngine;

public class ManagerScript : MonoBehaviour {

	public static ManagerScript Instance { get; private set; }
	public static int Counter { get; private set; }

	// Use this for initialization
	void Start () {
		Instance = this;
	}

	public void IncrementCounter()
	{
		Counter++;
		UIScript.Instance.UpdatePointsText();
	}

	public void RestartGame()
	{
		GooglePlayGameScript.AddScoreToLeaderboard(GPGSIds.leaderboard_leaderboard, Counter);
		Counter = 0;
		UIScript.Instance.UpdatePointsText();
	}

}

using UnityEngine;
using UnityEngine.UI;

public class UIScript : MonoBehaviour {

	public static UIScript Instance { get; private set; }

	// Use this for initialization
	void Start () {
		Instance = this;
	}

	[SerializeField]
	private Text pointsTxt;

	

	public void ShowLeaderboards()
	{
		GooglePlayGameScript.ShowLeaderboardsUI();
	}

	public void UpdatePointsText()
	{
		pointsTxt.text = ManagerScript.Counter.ToString();
	}
}

In my experience, the easiest way to create the functionality of a singleton in Unity is to have a public static instance of your script, and use the script’s OnAwake function to set the variable to be equal to the first instance that is created. Something like this:

public class MyClass : MonoBehaviour {
    public static MyClass instance = null;
    void Awake()
    {
        if (instance == null)
        {
            instance = this;
        }
        else if (instance != this)
        {
            Destroy(gameObject);
        }
    }
}

This will limit you to only having one instance of your script at any time.