Access to all issues on each individual project is open. All you need is a register for a free GitLab accoount.
Visit the issues page for the project that you want to report and issue with:
Ensure that your issue is not already reported.
If it is not, click on "New Issue" to open a new issue.
Add a meaningful Title, and as much information as you can in the Description, with supporting files.
Submit the issue.
Visit the issue board and assign a ticket to yourself