Follow the below steps to reject the candidate:

1. Go to the test analytics/report whose candidate you want to reject.
2. Click on the "Funnel" option present in the left vertical menu.
3. Click on "Submissions".
4. Click on "View Details" against the candidate to whom you want to reject.
5. Click on the "Action" option present on the top right corner of the page and then select the "Mark Rejected" option.
6. Candidates will be marked as rejected and will be reflected under the "Rejected" tab.