GitLab connects to Enzyme using a standard OAuth flow and will take just a couple of clicks. Enzyme will use the current users email address, so the Enzyme user must also have Maintainer or Owner access to the GitLab organization.
Ensure that you have selected the correct repository that you want to associated with the currently selected product.
And after linking, select the repository you would like to associate with this product:
Permissions & Repository Access
The GitLab repository must be private or public, Internal repositories won't be visible.
And the person creating the link to Enzyme will need to have either Maintainer or Owner permissions on the repository. Developer and below will be not be sufficient.
Now that the integration is setup you can use GitLab to populate the design control module in Enzyme.
This article covers daily use: How do I use the GitLab integration in my workflow?