Open the "FBI" homebrew application on your 3DS.
The game will appear as a new "gift" wrapped icon on your home screen. Download Crashmo | CIA File | 21M
When you see a "CIA" file, it refers to a specific format used by the Nintendo 3DS system. CIA stands for "CTR Importable Archive." Open the "FBI" homebrew application on your 3DS
Are you trying to play this on an or an emulator ? Do you already have Custom Firmware (CFW) installed? Download Crashmo | CIA File | 21M
These files are used to install games, updates, or DLC directly to the 3DS home menu.
To use a CIA file, a 3DS must usually have Custom Firmware (CFW) like Luma3DS installed.