Presumably, your merge request is about merging your fork master branch into the upstream master branch, right?
In that case, you have two options:
Go into the Gitlab settings of your fork, find the setting where branches are protected and disable the protection for your master branch
(the recommended way, at least for future merge requests) always create a feature branch, never work on master in the first place. You can create a branch from what you have right now on the command line with git checkout -b featurename. Then push that branch and create a new merge request for it