SDL Trados Studio 2015 deactivated during Windows 10 update

My Windows 10 update failed, so I'm back on Windows 8.1 Pro, but during the process, I did not deactivate my licence and now Studio is asking for reactivation. How do I proceed? Can't find anything about this in the KB, oddly. 

Single use SDL Trados Studio 2015 Pro licence, for what it's worth.

Thanks for any pointers.

Regards,

Karen Tkaczyk