Due to spam, new Gitlab users are set to [external](https://docs.gitlab.com/ee/user/admin_area/external_users.html). In order to do anything, you'll need to ask for your account to be promoted. Sorry for the inconvenience.
If you have any other questions, see this [forum thread](https://discourse.tt-rss.org/t/how-to-contribute-code-via-pull-requests-on-git-tt-rss-org/1850).