How to update new frame while another is computing?

Hi! I'm doing a checkers program and I want to show to screen the human while the program is computing the move of the AI. Here goes the transition between the Human and Computer move:

void FinishHumanMove(GivenMove givenMove) {

     ApplyMove(pieceOnBoard,givenMove);        
     UpdateBoard(); //Visual Update            
     ComputerTurn();

}

void ComputerTurn() {

     currentPlayer = WhoIsPlaying.Computer;
     GivenMove chosenComputerMove = MinimaxDecision(pieceOnBoard,7);        
     ApplyMove(pieceOnBoard,chosenComputerMove);
     UpdateBoard(); //Visual Update
     UpdateTileComputerMove(chosenComputerMove); //Visual Update
     HumanTurn();    
 }

However, because the computation time is quite long is the ComputerTurn() function, the UpdateBoard in the FinishHumanMove() does not finish, hence there is a feeling of lag. I checked the yield function and coroutine, but i don't know how to use them to solve my problem.

Any suggestion to how to finish the rendering of the UpdateBoard() while computing the ComputerTurn??

Thanks.