So far, you know how to add access_token to the notebook configuration file. There are other parameters that you can modify using that file. These are the default values:

c.GitLabConfig.allow_client_side_access_token = False
c.GitLabConfig.url = "https://gitlab.com"
c.GitLabConfig.validate_cert = True 

If you run your own GitLab instance, for example, update c.GitLabConfig.url so that it points to it.