I was working on an issue linked to a gitlab merge-request that I completed but I haven't been able to do it yet (I have to wait for some colleague to get free to review).
Now while I wait I should start working on a new issue but, to develop the functionality of this second issue, I need the files committed in the first issue.
So I decided to continue working on the same merge request and then review both at the same time.
I am sure there is a way to mark on gitlab that that merge request closes both issues but I don't remember how to do it and I have some problem finding such a specific operation on the gitlab documentation!
example of a merge-request closing 2 issues: