You can change the Mii set for your Mii Racing Suits by following the steps below.
1. Tap Menu, then tap on the Mii icon.
2. Tap the Mii Racing Suit for which you want to change the Mii on the Manage Mii Characters screen.
3. Tap the Mii icon in the upper right corner of the Mii Racing Suit.
4. Tap the Mii you want to use on the Choose a Mii screen.
Please see the articles below for information about how to add Miis to Manage Mii Characters or how to edit a Mii's face.
How do I add Mii characters?
I want to edit the face of a Mii character that I added.