First, 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 URLs below after your Confluence web address:
|Salesforce & Confluence Server Connector|
For example, to install the license for COM, access the following link:
Access the link and you should now be able to install the license.
If this still does not work, try restarting your Confluence instance.