First, try the
battery trick.
***
If you manage to gain access to
Luma3DS configuration by holding (Select) button when first turning on the 3DS.
Update the custom firmware depending what version you have:
Luma3DS v7.0.5 or older (arm9loaderhax):
Luma3DS v7.1–v9.0 (boot9strap):
- Updating B9S
- If you have Luma3DS v7.1, don't replace the boot.firm until after using SafeB9SInstaller.
- If you want to cheat a little collecting files, use the archive found here.
***
Once the custom firmware is updated, try updating the 3DS firmware with
Recovery Mode.
If that still doesn't fix the issue, do
CTRTransfer.
If that STILL doesn't fix the issue, do CTRTransfer but this time with Decrypt9WIP. See
here.