Solution:
You will need to use ninfs to mount the backup on a PC and then pull the movable.sed
out of the mount.
Ensure you have a copy of the file boot9.bin
, as ninfs requires it to work. This file can be obtained through fastboot3DS or GodMode9 on any working 3DS that has CFW installed, or from the folder sd:/luma/backups
on the SD card of a console that has previously been modded.