Making tig tag toe in c#

This is my 1st game and got told to make tig tag toe in c#. Iv got 2 player wolker :) but now trying 1 player (AI). but do not know where to start. Know the rules eg if center is empty, if plaery 1 has 2 in row block ......... but dont know how to get AI to click on button for 2 player i have

 if (GUI.Button (new Rect (100, 240, 50, 50), counter1, box)&& hasBeenPressed1)
             {
                 if (player == 1) 
                 {
                     counter1 = "X";
                     player ++;
                     turnCount ++;
                     p1row1 ++;
                     p1col1 ++;
                     p1cro1 ++;
 
                 
                 } else {
                     counter1 = "O";
                     player --;
                     turnCount ++;
                     p2row1 ++;
                     p2col1 ++;
                     p2cro1 ++;
             
             }
             hasBeenPressed1 = false;
             }

on each box can some one please point me in the right way thanks