You can manage your Isadora 3 license information using the web-based License Portal.
Access the License Portal via this link:
You can also access the License Portal from the Isadora 3 menu under Help > Go To License Portal
While on the license portal, you can:

The License Portal is especially useful when you do not have direct access to your previously activated computer(s). For example, should you need to activate your Isadora 3 license on a new computer after replacing a computer (or on the same computer after reinstalling your operating system/replacing some of the internal hardware), you can use the License Portal to deactivate your Isadora 3 license on your old system so that you can activate your Isadora 3 license on your new system.

The License Portal cannot be used to view or manage Isadora 1, Isadora 2, USB Key, or Sassafras licenses.