There are Pokémon like Snorlax or Necrozma that are just so large, they take up both screens of the 3DS in the Pokémon Refresh menu. The problem is, when I want to remove dust from him, I can't reach the top part of his body, which is stuck on the top screen. How do I reach the top part of such a Pokémon?
Take your stylus and place it on the top of your bottom screen. Then just hold the stylus there for a second or two. The screen will automatically scroll up and place the top of the Pokémon on the bottom screen. If you want to go back to the bottom part, you can do the same thing by placing your stylus on the bottom part of the bottom screen and holding it there.