If the threads, cord or mast shaft is damaged = replace it.
Antenna mast
MB# B6 6 82 8037
We have it in stock.
http://www.allpartsexpress.com/
If there is no damage:
* Turn the key on.
* Feed the cord into the power unit.
* Have an assistant turn the radio on then off.
* The mast should draw down.
* Screw the mounting nut back in snug.
Test the antenna extension/retract twice = radio on/off.