GitLab-The source branch is N commit behind the target branch

 # Add a remote named `upstream` pointing to the original repository

git remote add upstream https://gitlab.example.com/example/your_project.git

# Fetch the latest commmits from `upstream`
git fetch upstream

# Checkout our branch-A
git checkout branch-A

# Rebase our branch on top of the `upstream/develop` branch
git rebase upstream/develop

# If needed fix any conflicts that may have appeared and then `git rebase --continue`  

# Push the changes to the branch of your merge request
git push --force origin branch-A