To play Neo Geo games as CIA files on your 3DS home menu, you generally have two main paths: creating for a clean home menu look, or installing a RetroArch CIA for a comprehensive library management system. Option 1: Individual Game Forwarders (CIA)
Most Neo Geo emulators require a neogeo.zip BIOS file placed in the correct system folder (usually /_nds/ or RetroArch's system folder) to function. neo geo 3ds cia
RetroArch is the most powerful emulator available for the 3DS. It uses "cores" to emulate different systems. To play Neo Geo games, you need the core. To play Neo Geo games as CIA files