Pull the loose seam back gently until you feel a slight resistance where the wallpaper is well-adhered to the wall.
Apply a thin (no thicker than a piece of paper) coating of wallpaper repair paste to the underside of the paper, using a ½ inch paintbrush, making sure you have completely coated the loose paper.
Press the wallpaper back into place, smoothing the surface with the palm of your hand.
Wipe the reglued wallpaper with a damp sponge, working from the center of the sheet to the seam to press out any air bubbles.
Roll the seam with a wallpaper roller to ensure a tight seal. Allow to air dry.