Your feature or fix are currently done in your fork you must create a merge request on the upstream project for spreed your changes to others contributors.
In gitlab GUI open your fork (normaly in your namespace), if you've pushed your branch into your fork repository a new button has available in the GUI create merge request, so click on!
The page loading a new merging form, you must fill it! At start you must select the king of merge request in the selectbox available (example: doc/fix/feat) and respond to asked questions.