The Attendant Pro terms of service allow an authorization key to be moved to a new computer once every 30 days.

If you would like export the current user settings (including the authorization key) to be restored on a new computer, open the options window | Configuration Information Tab | Export Config File button. The exported user settings, including the authorization key, are per user settings.

To unregister, remove the authorization key from the Authorization key field in the Options window or uninstall the program.

On the new computer, open the Options window | Configuration Information | Import config file button.  After the config file has been imported, restart Attendant Pro.