Log in to Gemini and create a new user that Atlas will use. This user should have basic permissions only on the projects that you wish to expose to Atlas.

Once this user has been created, log in to Gemini with that user and click on the "Profile" (top right). Generate an api key and copy it.

Log in to Atlas as an administrator and go to the Gemini configuration section. Set the url, username and api key for the new Gemini user you've just created.

Go to the Tags section under Administration and edit each tag that requires Gemini integration. Simply select the appropriate Gemini project for the tag.