And it doesn't matter what I do, I can't get the Access Key to bring up the Miis from my old save. My original plan was to bring back all the Miis after I'd done this, but for some reason whenever you enter my Access Key it brings you to my new save instead of my old save.
So I made the account, brought over pretty much all the Miis from my old save, and beat the Darker Lord. So basically, I started a new save file a couple months ago on our OLED Switch but on my account since I wanted to redo the appearance of some of my team members but using other people's Miis.