==I Unlinked my NANDs and my NNID Doesn't Work (on my O3DS)==

'''What you need to fix it'''
EmuNand Tool: get it here: https://gbatemp.net/threads/emunand-tool-release-and-support-thread.359239/
Tiny Format: https://github.com/javimadgit/TinyFormat/releases
FBI installed on your Emunand. See earlier tutorials for the link, you should have it.
O3DS with '''emuNAND on 10.3'''

'''STEP 1'''
Use emuNAND tool to backup your emunand
Copy Tinyformat.cia to your SD

'''STEP 2'''
Launch FBI in your emuNAND.
Install TinyFormat.cia

'''STEP 3'''
Once installed, reboot back into your emuNAND.
Find TinyFormat on the home menu, and run it. '''THIS WILL FORMAT your emuNAND to factory defaults'''
(files on your normal SD partition will remain untouched)

'''STEP 4'''
Reboot back into your emuNAND
Configure everything as-is normal.
Go to Settings -> NNID Settings
Link your NNID.

'''STEP 5'''
Use emuNAND Tool to inject your emuNAND backup to your SD card
Boot your old emuNAND
Try to access eShop.
Did it work? Cool.

>Why does this happen?
When you format your 3DS sysNAND, you have to connect to the internet. This way, it can tell Nintendo you have signed out. You need to re-link it with a 3DS in the initial setup phase, but your emuNand already thinks it is linked. You have to re-link it on up-to-date firmware, so we format our emuNAND to establish a link (since we can't use sysNand for this), then use our old emuNand to connect as normal.