Retesting mistakes in Bitsboard is really simple and easy.  Anytime you launch a board, you are instantly given the option to study all items, only the favorite items, or only the recent mistakes.  

To study only the previous mistakes, select the option called "Study ✘".  If you have not previously played a board or the user got every item correct for the selected board, then this option does not appear.  "Study ✘" only appears if the user previously answered a question incorrectly.

In the example above, when you press on "Study 2 ✘" you will be shown only the 2 items that the user previously got wrong for the selected board.  

To review all bits in the board, make sure that "Study All" is the selected option.

To review only your favorite bits (i.e. those you want to focus on right now), select Study ★.  The favorites option only appears if you have previously selected any favorites.  If you are not familiar with how to select favorites, follow the link below.