If you download a game in CIA format and it's not got the game key inserted just convert it with Batch CIA 3DS Decryptor , after converted just run it on Citra software as a normal 3ds game
I think you should try nintendo 3ds emulator for android The Nintendo 3Ds require an emulator for it to work, such as a flash cart or the newly developed Citra 3Ds emulator, which requires the user to download Citra ROMs. Users can use the Citra 3Ds emulator by ROMS downloads and running those ROMs on the Citra Emulator.