How do you re-catch lugia in alpha sapphire?

To re-catch Lugia in Pokémon Alpha Sapphire, you'll first need to access the location where it appears. After defeating the Elite Four and completing the main storyline, head to the Seafoam Islands. Use the Surf ability to reach the cave where Lugia resides, and save your game before entering. Once inside, you can encounter it again, so be prepared with Ultra Balls or a Master Ball to increase your chances of capturing it.