You need to extract your save via JKSV and copy the BCAT folder to your PC.
Next, download the Event BCAT and extract the directories folder.
Put the directories folder inside your BCAT save folder next to passphrase.bin.
Copy it back to your switch and restore the BCAT.
You’ll know it was successful if on the title screen, the version number has a letter after it e.g. 1.2.1c
Edit: Spelling.