Repairing wallpaper seams that have lifted due to adhesive failure takes time.
Repair with this fix:
1. Get the seam wet with hot water to the curled, rolled, separated wallpaper. It soaks in. Keep applying hot water but wipe dripping or excess. Do until paper is pliable to lie flat.
2. Gently lift the wallpaper at the seam using a putty knife or wallpaper scraper.
3. Squirt glue along and into the seam, move with putty knife.
4. Press along the seam with damp towel, wiping up glue. Get all the glue.
5. Use a dry towel to keep pressing until the glue cures enough to hold. Get it flat and smooth.
6. Masking tape may hold a wet seem, but Gorilla tape may be too strong.