There is no way to install the Linking license?
Please check that the add-on has been installed successfully and enabled.
Then refresh the Confluence Administration page.
If you still cannot see the ServiceRocket Plugin menu (so you can install the license), try appending the URL below after your Confluence web address:
Access the link and you should now be able to install the license.
If this still does not work, try restarting your Confluence instance.