Trapped air bubbles and blisters are almost always caused by an installation problem. Often, a speck of dirt or paint chip keeps the paper from bonding and allows a bubble to form with time and humidity. Or, the installer didn't force out all of the air. Either way, the only cure is to cut open the blister, release the air and reglue the spot.
Most bubbles and blisters are just air pockets, but it pays to check. Press a finger against the bubble. Feel a speck of something? Cut an X through the paper and remove it with tweezers or a razor knife. Then, squeeze seam adhesive through the slit and roll the paper flat.
If the bubble really is just air, you can fix the problem with a glue-injecting syringe; it makes a less-conspicuous repair than cutting a slit. We bought ours, an Advance Equipment Co. model, at a Sherwin-Williams paint store for $5.50.
Fill the syringe with seam adhesive, push it directly into the bubble and press the plunger. On some vinyl wallcoverings, forcing in the needle will stretch the vinyl. If it does, cut a tiny slit with a razor knife (photo 6). Then insert the needle and squirt in the adhesive (photo 7). Finish off by flattening the repair with a seam roller and carefully wiping off any excess adhesive.