1. unpack the .f32 terrain file into the root folder of the 3dxstudio.
2. go to the command tab in 3dxstudio.
3. enter change-region myregionnamehere
4. cmd to enter -> terrain load myfile.f32
That's it the terrain of that region will now be as set.
If you want to provide a package already set with the terrain in place. Edit the Region.xml file in the regions table and change the default_terrain="filename.f32" value to the name of the terrain. This will make the default that file you put in the root directory.