Hello Sacco-dylan,
I actually just added Notation to the game today! you would need to re-download the game to be able to use Notation. To use it just press the A and B (A+B) buttons at the same time. than you can use the D-Pad and the A button to navigate on the smaller grid and show/hide Notation Numbers, then use the B button the exit Notation mode and go back to normal. This is the first iteration of this feature for now, and it doesn't look perfect because the boxes are really small so its hard to fit 9 numbers into them, but I figured this was better than nothing for now.
Thanks for playing my game and leaving feedback!! if you have any other ideas of what to add or how to improve the game please let me know.