In general, there are two ways for changing the domain of your license:
1.) Plugin settings
The recommended way would look as follows:
- Deactivate your current site via plugin settings (tab “licensing”)
- Remove your license key, click “Save Changes” and afterward uninstall the plugin
- Install the plugin on your new site and activate it by entering your license key again
2.) Account page
In case you don't have access to your old site anymore, don't worry.
Log into your account page, locate the order your license belongs to click on “View Licenses” on the right side of the screen.
On the next screen, click on “Manage Sites”.
Here you can remove your old domain. Afterward, add the new domain to the license (in the best case directly via plugin settings).