If you have the PC programming lead, you can use the software to re-program the programming extension.

If you have a punch down tool and a telephone socket and a little length of cable, you can punch this down on each extension in the CCU/ext ports module in turn until you find the extension you moved it to.

Punch down tool for sockets and the CCU connections:





The CCU has EXT terminals marked A B C D, these correspond to 2 5 1 6 on a master socket (although a secondary will work fine with a featurephone, but won't allow a standard phone to ring).

If you punch down telephone cable from ABCD to 2516, you should get a featurephone working on that ext port.  Try all eight own the main CCU, and any in the expansion ports module (if you have one).

If you don't have the programming lead, hunt for it.  BT normally leave it.  Look, under all covers on the CCU, and with your site documentation.  The software can be obtained easily enough via BT, I think there's even a download on their site these days.

There is no way to do a cold hard reset other through the programming mentor software.