Once your wallpaper has dried, cut out the bay openings and proceed with staircase installation. This process can be challenging due to the precise fit of laser-cut dollhouse parts, which may have swollen from paint and stain. To ensure success, build a sturdy dollhouse shell and staircase, as you'll likely need a mallet to tap the staircase into place.
Use a long, thick dowel or similar strong object to reach inside and gently but firmly tap the staircase into position. Apply force as needed, but be mindful of the wallpaper. Any damage can be easily fixed with scrap pieces and a glue stick but it's best to avoid doing so if possible. You may also need to touch up the floor stain afterward.
After securing the staircase, cover the second floor tabs with wood filler. Allow it to dry overnight before sanding smooth. Once dry, the filler will accept stain more readily. Finally, touch up the ceiling around the staircase assembly as necessary.