Select SD -> cias (or wherever you placed them). Install Files:
Place your CIA files anywhere on your 3DS SD card (e.g., in a folder named cias ). SteamWorld Heist: DLC & Update 2.0 3DS (EUR) CIA
The DLC content blends into existing save files. You do not need to start a new game; the mission "Fully Loaded" (marked with a unique logo) will appear on your map. Select SD -> cias (or wherever you placed them)