I don't know much, but you can try this. https://gbatemp.net/threads/release-inject-any-app-into-health-safety-o3ds-n3ds-cfw-only.402236/I have rxtools installed but have problem with install of FBI, checking TMD returns failed.
Thanks for info.
I can confirm it works on N3DS.Assuming you have N3DS. Works dandy on O3DS. Helped a friend with the downgrade and install of FBI into emunand afterwards.