EXFO FTB-500 (Window XP) - Manual (Page 285)

Troubleshooting
FTB-500 275
Restoring Your Unit to Normal Operation
4. From the main window, select Restore system partition from an
image, then tap Next.
5. Select which image (.wim file) you want to use. An image file is
available on the E drive. However, you can use an image file that you
have on a USB storage device. Use the Browse button to locate the
image file that you want to use.