You can attempt to connect to it with the default settings,
The defaults are:
Default Gateway IP: 192.168.190.1 this ip will always listen unless someone configured it to be something else..
Default username: adm1n
Default password: blue1socket
Default subnet mask: 255.255.255.0
Default DNS server: 192.168.190.1
Unfortunately there is not a way for the end user to reset the unit to factory defaults, only Adtran can do that on these units, you may have better luck contacting Adtran support on this issue.