: CIA stands for CTR Importable Archive. These are files used to install games and homebrew (custom, unofficial software) on the Nintendo 3DS. They are typically used in the context of homebrew and piracy, as they allow users to install games without purchasing them through the official eShop.
Not sure if you’re already running v1.2? Checking is simple: Launch Pokémon Ultra Moon . pokemon ultra moon update 12 3ds world cia