How do i slow down the game (othello game)??

Hello, I built an othello game that can be played by 2 humans , human and computer and two computers.

Everything works correctly but the problem is that when 2 computers play with each other the fram doesn't appear until the game is finish.

I think it is becase the 2 computers is very fast, for that i tried to use the timer but it give me many errors and the result of the game is completely wrong. also i used the (thread.sleep) but it didn't solve the problem...

can you help me please..

thank you