When the computer makes a winning move because of your last move or when you accidentally make the wrong move, you can undo your last move and change it. To undo your last move, press the button in the header bar which either shows an arrow and the color to play or says End!, and select Undo last move, or press CtrlZ. You can now drop your marble at a different row in the game area to change your move.

If you are not sure of your next move, you can use a hint. When you use a hint, your marble moves to the top of the column that is the best choice, strategy-wise, and blinks. You can then drop your marble into that column. To use a hint, press the button in the header bar which either shows an arrow and the color to play or says End! and select Hint, or press CtrlH.