A simple and easy tutorial to restoring your NAND backup.
This restoration method assumes that you have access to gateways latest "Ultra" menu.1.) Make sure you have your NAND.BIN is placed on your 3DS's SD.
2.) Launch the GW menu (the one where it has NAND backup, etc)
3.) Hold up while pressing "Downgrade" and you should be asked to restore the NAND backup to sysNAND.
Easy as 123! If you were...
[TUTORIAL] Restoring NAND WITHOUT hardware method