Start on production branch and create new branch from it (e.g. branch hotfix-20200615)
Cherry pick commits from master branch (git cherry-pick {commitId})
picking commits from MRs / branches that have not been merged into master creates differences between master and production that will be annoying in the next release
optionally check git log history and diff (e.g. git diff origin/production)
add new hotfix section to changelog
there might be other merge conflicts in the changelog -> fix them manually (maybe change auto merge for the changelog in the future?) and commit
the hotfix branch can be pushed to run the pipeline and to check if the tests are ok
merge your changes back into the master branch: git checkout master; git merge production (don't forget to update your local branch before)
possibly, you get conflicts here to be solved. It is important to do that now and not at the next release, so the person doing the next release is not annoyed :-)
make the changelog nice again and commit it into the merge commit: git commit --amend