There is no physical access to the ProxySG so serial connection is not possible. However, the current admin password is unknown and needs resetting. If this is attempted from the management console, the old or current password is prompted, which is an issue, because it is unknown.
No particular errors are seen except for the fact that admin password cannot be reset and the current one is unknown.
Connect to CLI remotely using SSH (port 22)
Login with any user that has admin rights, e.g. local realm AD user
#(config)security username admin
Alternatively this can be done via Management Center or Director by creating a script/overlay to push out the commands