GitLab CI Variables

How do I trigger an update to a GitLab Merge Request’s build status? I’m running tests and having the main job report the success or failure of those tests. In addition, I want to send the coverage information I generate to another service to analyze whether the coverage has improved or not, and report back and update the merge request with an additional build status. How do I access the merge request id from the CI variables? Is that even possible? What other options do I have for knowing the id of the merge request I need to update?