Novamura was advertised as the paper youy could hang and peel off and rehang.
They even showed novamura being put into a washing machine for cleaning prior to rehanging.
If the paper has been left in situ since first hanging it should peel to leave the original backing on the wall.
If it has been peeled and rehung without original backing or lining paper there will just be adhesive.
Either way for water based adhesives, the route is to soften the adhesive with water or steam.
As you say steam is not working, It may be more appropriate to pierce the whole surface with a proprietary tool or to use 40 grit glass paper.
Then gently sponge the surface of a single drop to moisten the adhesive, and repeat until the paper peels off. Be patient, if you have pierced the outer surface eventually the adhesive will soften.