Hi,
If you know, where it should be placed, you can just move it to the C drive (the right folder). Or you can delete the library from the D drive, and install it again to the default C drive. Then you are sure, the library is on the right place.
As a workaround, to have the library on an other drive is to make the aliases files of all libraries files, and move it to the default folder, where the files spouse to be. Cubase can find the alias (which is very small file), and the large files are stored on the other drive.