If you have a seam that’s coming apart, reactivate the paste around the gap with a rag soaked in warm water. Hold the rag over the area for a minute or two, and then carefully open the gap a little larger so you’ll have more room for the sealer. Squeeze seam sealer (white glue works in a pinch) into the gap, and press the paper to the wall with a roller. Clean off the excess sealer with a sponge.