Haven't played it, so not sure if it saves to the game cartridge or the 3DS. You can check your 3DS's SD card by going to system setting and then Data Management. If you see any save data, you can erase it and it'll be like starting a new game.

If there's nothing there, try holding all the face buttons (A+B+X+Y) when starting up the game. This is usually the way to delete data off game cartridges with a lot of DS and 3DS games. Hopefully this helps.