After some time, the merge request is open in the project , it is normal that the version of the branch that you are trying to merge becomes outdated due to the fact that other people merge their changes into it.
Gitlab helps you by showing how far the version of the updated branch is behind the remote branch.
, rebase , . , , . , , , .
rebase , :
git remote add upstream https://gitlab.example.com/example/your_project.git
git fetch upstream
git checkout branch-A
git rebase upstream/develop
git push --force origin branch-A
: , , .