Get the image URL of the dragon/scry you're previewing the accent on. Put this in the first text field.
Select the skin you want from the dropdown.
Optional: get a transparent apparel URL. to do this, go to the dressing room, import the apparel you want to preview, and add a Marva's Invisibility Cloak at the very bottom. Then copy that image URL.
This previewer does not automatically mask primal or multigaze eyes, for best results, please scry dragons with eye types which do not break eye lineart.