EXFO FTB-500 - Manual (Page 163)

Managing Data
FTB-500 155
Using the USB to RS-232 Adapter
3d. Under Devices and Printers, tap Device Manager.
3e. Expand the Ports (COM & LPT) list to retrieve the COM port
number that has been assigned to the adapter (identified as USB
Serial Port) and write it down.
3f. Close the Device Manager.