1) Go to your account area https://www.8theme.com/account and register the second purchase code there
2) Check the screenshots in the private content area.
Remove theme from these domains if you want to use the licenses for other projects. Reply back once you remove the theme from these domains, not just deactivate the license in theme settings.
One standard license is valid only for 1 project. Running multiple projects on a single license is a copyright violation.