Are you seeing a (like "encrypted ROM" or "missing font")? I can provide a step-by-step guide for your exact setup.
While I won't provide direct links to download a 3DS BIOS file, I can suggest some alternatives: 3ds bios file download for android
within the emulator's root directory on your internal storage. : If you are using a 3DS "core" within , BIOS files must be placed in the RetroArch/system Are you seeing a (like "encrypted ROM" or "missing font")