get godmode9, start 3ds with start button and power button.
Press home button go to "Scripts", choose GM9Megascript, then select "Scripts from Plailect's Guide"
choose "Setup Luma3DS to CTRNAND" confirm it with A, then it tells you that SysNAND is locked and you have to unlock it by confirming with A and imput the shown pattern.
After that it should be done.