Use Hourglass9 or Decrypt9 to inject it into SysNAND. I recommend Hourglass9.
Files we'll need:
Universal Inject Generator:
https://github.com/d0k3/Universal-Inject-Generator/archive/master.zip
FBI:
https://github.com/Steveice10/FBI/releases/
The following steps are for Decrypt9, Hourglass9 should be somewhat similar and easier. I am just copying and pasting from my own guide, since I rather not type out everything again lol. The concept should be similar in both though.
1. Go to "SysNAND Options", then "Miscellaneous...", then select the "Health & Safety Dump" option to dump Health & Safety to hs.app.
2. Once done, Press B to return to the menu, then press Select to safely eject your SD card.
3. Put your SD Card into your computer.
4. Extract the contents of the Universal Inject Generator .zip to somewhere on your computer.
5. Then copy both hs.app from your SD card and FBI.cia from the FBI zip to the input folder.
6. Double click go.bat (or execute go.sh with Terminal on Linux, or double click Mac_inject_launcher.app on Mac)
7. Copy FBI_inject_with_banner.app to the root of your SD card and reinsert your SD card into your 3DS.
8. Press B on Decrypt9, while still in "Miscellaneous... (SysNAND)", select the "Health & Safety Inject" option. (Otherwise go to "SysNAND Options", then "Miscellaneous...", and select the "Health & Safety Inject" option.)
9. Enter the button confirmation.
10. Press down once and make sure it has selected FBI_inject_with_banner.app, then press A and wait for it to finish injecting.