If you're able to select the correct GitLab organization in the PullRequest dashboard, but none of the expected projects are visible in the context drop-down or on the organization's home screen, you may need to set a Public email setting in GitLab.
Open GitLab and select User settings -> Profile.
Find the Public email field in the Main settings section.
Open the drop-down and select the same email address assigned to your PullRequest account.
Your projects should now be listed in the PullRequest dashboard.