If it's dead, nothing you can do about it.  It's not replaceable like the front panel I/O board.  Put a small piece of electrical tape over the dead port to prevent accidental use, creating confusion for user.
I bought it refurbished and it looks like new internally and externally. It’s not a bent pin, dirty port or driver issue as the other ports work and the single defective port is defective in both Windows and Linux. Is there anything I can do? I for just 4 ports on the back. 
Single dead rear USB 2.0 on 3050 SFF