Dressed To The Nines requires you to use chapter select to replay through Chapters 3, 8 and 9 once you have finished the game, as explained in more depth throughout this page.
There are three different dresses per character, making for nine dresses in total, with each character having a different method of unlocking the dresses.
Watch on YouTube How Dresses and the Dressed to the Nines Trophy work in the Final Fantasy 7 Remake