Go to File > Install CIA and select your decrypted Pokémon Y Update 1.5 file.
A genuine "Pokémon Y Update 1.5 Decrypted 3DS EUR USA Repack" should contain the following file structure when extracted: pokemon y update 15 decrypted 3ds eur usa repack
Leo’s bedroom light flickered. His computer screen went black. And from the 3DS speakers, very softly, came the sound of a single Poké Ball snapping shut. Go to File > Install CIA and select