This may not be how it works NOW, but the way you used to be able to do this was to invoke the "Deactivate everywhere" option. I suspect this is no longer present since the swing to CLOUD so the standard procedure now is to contact Customer Support either by chat or via phone when you have serial number and activation issues. They should be able to manage the deactivation for you.
Here is a link to a page with options to help make contact: