Ahhhh, How exciting!! I'm wishing you lots of luck and fun with your project <333 I tried outlining my process down below but feel free to contact me via Discord (or e-mail) if you have more specific questions! ^^
The base for my dress-up games is a parallax image. When drawing the parallax image, I have a 48x48px grid on, so I know the best posititions to place my buttons and stuff.
After that, I have the dress-up options on a transparent image of the same size. All dresses are on image layer 5, all flowers on image layer 6 etc - this way they replace wach other whenever you choose a new outfit.
When you click on the arrow, the game checks which dress is presented (there is a variable counter) and then just loads the next image.
And honestly, that's it?? When working with image layers, I also always recommend to fade the pics in/out, so the engine has some time to load them! Otherwise you end up with the first image dissapearing and the second image just plopping in. (I didn't do that in this game though because it can be rather time-consuming lmao)