Setup ReiNAND, then rename the "arm9loaderhax.bin" to literally anything, let's go with "ReiNAND.bin."
From there you can either launch it as Luma3DS payload or as a payload from whatever bootloader you are using.
You would place the SD card into the computer. From there download the latest ReiNAND from the repo and the latest firmware.bin from the
repo as well (under the "data" link.) With all of that, copy the firmware.bin into "rei" folder, replacing the one already in there. Then copy the "arm9loaderhax.bin" and "rei" folder onto the SD card, replacing the ones already on there.