This is likely what you are looking for if you searched for "Neo Geo 3DS CIA." This method creates a specific CIA file for one specific game . When installed, that game appears as its own icon on your 3DS home menu.
With the Neo Geo BIOS and games installed, you can now enjoy a wide range of classic titles on your 3DS, including:
Once completed, press the Home button. A new gift icon wrapped on your HOME Menu signifies a successful installation. Comparing New 3DS vs. Old 3DS Performance
Installing a is one of the best upgrades you can give to your Nintendo handheld. It bridges the gap between the Nintendo aesthetic and the high-octane 2D action of SNK's golden era. With a well-configured RetroArch installation, your 3DS becomes the ultimate portable arcade.