To install a CIA file, your Nintendo 3DS must be running custom firmware (CFW) with Luma3DS and the FBI file manager installed. Step 1: Transfer the File Power off your 3DS and remove the SD card. Insert the SD card into your computer.
The specific file you mentioned is a .cia (CTR Importable Archive) version, typically used for installing software on custom firmware-enabled 3DS systems or emulators like . Pokemon Omega Ruby- Update 1.4 3DS -USA- CIA -R...
To help you get your game running perfectly, please let me know: To install a CIA file, your Nintendo 3DS