To install and activate the server extension, follow the steps mentioned here:

1. Install the server extension using pip in the Terminal, and then enable it using the following command:

pip install jupyterlab-gitlab

2. If you are running notebook 5.3 or later, this will automatically enable the extension. If it doesn't, then enable the server extension by running the following command:

jupyter serverextension enable --sys-prefix jupyterlab_gitlab

3. To check whether the server extension is enabled, run the following command:

jupyter serverextension list

4. Now, you can add the credentials you got from GitLab to your notebook configuration file. Instructions for generating a configuration file can be found here: https://jupyter-notebook.readthedocs.io/en/stable/config_overview.html#configure-nbserver. Once you have identified this file, add the following line to it:

c.GitLabConfig.access_token = "< YOUR_ACCESS_TOKEN >"

In the preceding command, < YOUR_ACCESS_TOKEN > is the string value you obtained previously.