To restore factory defaults on Cisco Unity Express firstly take the module offline by typing “offline“, then when confirmed issue the “restore factory defaults” command.
An example follows :
Router# service-mode  service-engine 1/0
Trying 192.168.n.3, 2006 … Open
se-192-168-n-3# offline
!!!WARNING!!!: If you are going offline to do a backup, it is recommended
that you save the current running configuration using [...]