Launch Luma Updater (you should have it installed if you followed Plailect's guide) and wait for it to load
Once loaded, select the "Install latest hourly ([hourly version])" option.
Wait until it's done and it will ask to reboot.
Next, open FBI
Select the SD option, and scroll down until you see "arm9loaderhax.bin" (make sure you don't select the backup which should have a ".bak" extension instead) and press A
Next, select the "Copy" option.
Press B to return to the main menu, then select the CTR NAND option.
It will ask if you are sure about modifying files in the CTR NAND, just say yes to that.
Next, select the "<current directory>" option, and select "Paste" afterwards.
You should now have Luma3DS on your NAND. To test this, try turning your 3DS on without the SD card inside
EDIT: After booting your 3DS without the SD card in, you will be prompted to the Luma3DS configuration menu. This is normal if you updated Luma3DS on your CTR NAND, or if it's the first time you test it out. It should only ask you once.