If you have Luma3DS installed, you can use the encrypted version, but here is how to apply it if you only found a decrypted CIA:
If you strictly want to run the .3ds file (e.g., via the TwilightMenu++ homebrew app): pokemon x update 15 decrypted 3ds eur usa updated
This specifies the source format, pointing to native Nintendo 3DS files rather than converted digital install formats like .cia . If you have Luma3DS installed, you can use
on how to apply this update to a particular emulator or console? How to Update Pokémon X and Pokémon Y | Nintendo Support Doing so will cause a black screen or a crash on boot
You cannot apply an EUR update to a USA base ROM. Doing so will cause a black screen or a crash on boot. Always check your base game’s region in your emulator or 3DS FBI info panel.
He injected it into his old European 3DS—a beat-up blue console with a cracked hinge and a Pokémon X cartridge that hadn’t been ejected since 2014. The update installed in 0.7 seconds, faster than any official patch.