There are several programs which can create normal maps from diffuse texture, some freeware and others not. GIMP has a plugin which is easy to use, I believe Blender might be capable of doing it also, although there is a steep learning curve. Materialize is another free software which can create several different type maps including normal maps. ShaderMap is another program which can also create multiple maps although it is not free but modestly priced. I believe they might be offering a free version. And there is an online site which can convert your maps and allow you to save the results to your hard drive, also free (https://cpetry.github.io/NormalMap-Online/). Those that I mentioned are programs that come to mind, however, there are much more available if you conduct a search.
In the Material Room, if you use the PoserSurface panel, you connect your normal map to the Gradient_Mode Node and use the Tangent Space Normal Map setting. One the PhysicalSurface panel, you use the connecting node name NormalMap.