Cyberdata Voip Speaker help?

Hi folks
Having an issue with a client in the UK who has 30 extensions, and a cieling speaker. the speaker from today is permanently engaged.
I can access the PBX remotely no probs, and the extension is unregistered.

Is there a way, via putty, i can remotely stop and restart (reboot) just this extension without afecting the other extension on the system which are all fine?
I have no idea what sip commands i would use.

Thanks in advance
LH

*CLI> sip unregister should unregistered the extension.

The device should auto re-register after a timeout.

Are you saying that within asterisk I type sip unregister?

Yes.

You will need to add the extension number at the end of the command.