I am trying to do a connect four game and i am trying to make a dropDisc function. I have writen this:

Question

This is the GameViewModel:

data class Disc(var color: Color){

}

class GameViewModel:ViewModel() {
    private val boardWidth = 7
    private val boardHeight = 6
    private val emptyDisc = Disc(Color.White)

    private val _board = mutableStateListOf<List<Disc>>()
    val board: List<List<Disc>>
        get() = _board

    private var currentPlayer = Color.Red

    fun dropDisc(columnIndex: Int) {
        val column = _board[columnIndex].toMutableList()
        val emptySlot = column.indexOfFirst { it.color == Color.White }

        if (emptySlot != -1) {
            column[emptySlot].color = currentPlayer

            currentPlayer = if (currentPlayer == Color.Red) Color.Yellow else Color.Red

            _board[columnIndex] = column
        }
    }
}
//This is my GameScreen

@Composable
fun GameScreen(
    gameViewModel: GameViewModel= viewModel(),
){
    ConnectFourGame(gameViewModel = gameViewModel)
}

@Composable
fun BoardView(board: List<List<Disc>>, gameViewModel: GameViewModel){
    Box(
        modifier = Modifier
            .background(Color.Blue)
            .padding(4.dp)
    ){
        Column {
            for(row in 0 until 6){
                Row(
                    verticalAlignment = Alignment.CenterVertically,
                    horizontalArrangement = Arrangement.SpaceEvenly
                ){
                    for (column in 0 until 7){
                        Box(
                            modifier = Modifier
                                .size(50.dp)
                                .padding(4.dp)
                                .background(
                                    color=board[column][row].color,
                                    shape = CircleShape
                                )
                                .clickable {
                                    gameViewModel.dropDisc(column)
                                }
                        )
                    }
                }
            }
        }
    }

}


@Composable
fun ConnectFourGame(
    gameViewModel: GameViewModel = viewModel(),
){
    val board = gameViewModel.board

    Column (
        modifier= Modifier
            .fillMaxSize()
            .padding(10.dp),
        verticalArrangement = Arrangement.Center,
        horizontalAlignment = Alignment.CenterHorizontally
    ){
        Text(text = "Connect Four Game")
        Spacer(modifier = Modifier.height(16.dp))
        BoardView(board = board, gameViewModel = gameViewModel)
    }

}

I have wirtten the dropDisc as you can see but it doesnt want to work so i dont know what i can change?

I have written the code as you can see, i want the circle to change color to red then yellow when clicking on a empty circle. I have to write more but i feel like i already have explained but it doesnt let me post.... I have other parts like resetboard on the code but i couldnt put in in here