Download the Region Free Update 1.2 CIA from a verified repository such as the hShop Updates Directory.
The standard open-source title manager used to install CIA packages. pokemon ultra sun update 12 3ds world cia free
If you are using a Rom Hack (e.g., "Supernova Sun" or "Photonic Sun"), you may need to be careful. Some Rom Hacks explicitly warn because the official 1.2 patch can overwrite the hack's changes, causing crashes or breaking the mod. Download the Region Free Update 1