How to make the computer be the player 2 in C#?

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C#

game

I have this Tic Tac Toe Game, it works fine, however I am player 1 and player 2, I am playing with myself. I have been trying to make the computer to be player2, and to be smart enough to block if player 1 (me) has two Xs or two Os in a row, but I haven't been unsuccessful. Any ideas, please? Thanks.

This is the Code in C#

using System;
using Xamarin.Forms;

namespace TicTACTOE
{
    public partial class MainPage : ContentPage
    {
        private Button[] buttons = new Button[9];
        private GameDriver game = new GameDriver();
        private GameState gameState= new GameState();

        public MainPage()
        {
            InitializeComponent();        
            buttons[0] = button1;                      
            buttons[1] = button2;          
            buttons[2] = button3;           
            buttons[3] = button4;          
            buttons[4] = button5;           
            buttons[5] = button6;           
            buttons[6] = button7;         
            buttons[7] = button8;           
            buttons[8] = button9;
        }

        private void Button_Clicked(object sender, EventArgs e)
        {
            game.SetButton((Button)sender, this.gameState);
            if (game.CheckWinner(buttons))
            {
                gameOverStackLayout.IsVisible = true;
            }
        }

        private void PlayAgain_Clicked(Object sender, EventArgs e)
        {
            game.ResetGame(buttons);
            gameOverStackLayout.IsVisible = false;
        }
    }
}

and this is the other namespace

namespace TicTACTOE
{
    using Xamarin.Forms;

    internal class GameDriver
    {
        private PlayerType player = PlayerType.Human;

        private readonly int[,] Winners = new int[,]
        {
            {0,1,2},
            {3,4,5},
            {6,7,8},
            {0,3,6},
            {1,4,7},
            {2,5,8},
            {0,4,8},
            {2,4,6}
        };

        public bool CheckWinner(Button[] buttons)
        {
            bool gameOver = false;
            for (int i = 0; i < 8; i++)
            {
                Button b1 = buttons[Winners[i, 0]];
                Button b2 = buttons[Winners[i, 1]];
                Button b3 = buttons[Winners[i, 2]];

                if (b1.Text == "" || b2.Text == "" || b3.Text == "")
                {
                    continue;
                }                    

                if (b1.Text == b2.Text && b2.Text == b3.Text)
                {
                    b1.BackgroundColor = b2.BackgroundColor = b3.BackgroundColor = Color.Aqua;
                    gameOver = true;
                    break;
                }
            }

            bool isTie = true;
            if (!gameOver)
            {
                foreach (Button b in buttons)
                {
                    if (b.Text == "")
                    {
                        isTie = false;
                        break;
                    }
                }
                if (isTie)
                {
                    gameOver = true;
                }
            }
            return gameOver;
        }

        public void SetButton(Button b, GameState gameState)
        {
           
            if (b.Text == "")
            {
                b.Text = player == PlayerType.Human ? "X" : "O";
                player = player == PlayerType.Human ? PlayerType.AI : PlayerType.Human;
            }
        }
        public void ResetGame(Button[] buttons)
        {
            player = PlayerType.Human;
            foreach (Button b in buttons)
            {
                b.Text = "";
                b.BackgroundColor = Color.Gray;
            }
        }
    }
}

What I have tried:

I have tried

-to do this for each one of the buttons
-

//Button button1 = new Button();
           //button1.Clicked += Button_Clicked;

But, it doesn't work, either. Thanks