The Test Studio license is associated with the machine on which it is activated and it cannot be activated on another machine in the same time. However, there are certain occasions when a machine with an activated license cannot be accessed anymore - thus the used license cannot be deactivated.
To free up the seat and use the license on another machine, you can manually delete the old license key from your Telerik account and re-generate a new one for the new computer. Refer to the below listed approach how to proceed.
Log on to your Telerik account to the Manage Test Studio Activation Keys section.
Locate the license activated on the machine, which is no longer accessible and delete your old key. This will free up a slot allowing you to activate the license on any other machine.