A wrinkle sounds like a minor defect on a drywall-covered wall, and it usually is. It may have occurred because the drywall got wet, but if the drywall has dried out, and if it’s only a wrinkle, the repair is easy to accomplish. Wrinkles are more commonly the result of imperfectly taped seams. Drywall tape can separate from the wall when there isn’t enough mud underneath it. In that case, if it’s only a wrinkle, the repair is straightforward. Either way, you may have to do a little cutting before you cover the wrinkle with mud.
Cut out the wrinkled drywall paper or drywall tape, using a utility knife. Pull the paper or tape back to the point where it is still firmly attached to the wall.
Cover the damaged area on the drywall tape with a coat of drywall joint compound and lay a small piece of paper tape on top of it. Soak the tape in water before you apply it to help it stick better. Scrape the tape flat with a drywall knife. Remove excess mud.
Sand a wrinkled area on drywall paper with 120-grit sandpaper to eliminate fraying around the edges. Spread a coat of drywall primer on the exposed core, using a paintbrush. Allow the primer to dry completely. Trowel on a coat of mud and scrape it flat with a drywall knife. Allow the mud to dry completely, about 12 hours.
Recoat the repair — whether on drywall paper or on tape. Scrape the second coat as flat as possible. Let it dry and apply a third coat, if necessary. Scrape that coat flat.
Smooth the final coat with 120-grit sandpaper, then cover the repair with drywall primer. Paint it when the primer dries.