In order to allow candidates to raise requests for additional shifts (eg - the client requested them to work additional shifts on their existing assignment), the Allow workers to request new shifts should be ON from Settings >> General.

When candidates submit shift petitions, you will find it on the Shift Requests menu.

Click on the pencil icon next to the shift petition to view the request.

You can Reject or Confirm the request, or Cancel to review it again for later.