Once you have submitted a design request, the designers are being notified from Hunch.
When they are satisfied with what they have created, they can send you a notification vis Send & Request Review button from studio.
You will be notified on email when they do so.
When you open a design you can just leave a comment as a Supervisor. You can do so by hitting a button at the bottom left corner and leave a pin on the canvas. That will open a text box where you can type your feedback and leave it for the designer.
When you are satisfied with the comments that you have left, you can click on Send Feedback which will notify the designer to continue with their work.
This process will repeat until you are satisfied with the outcome of your request.
When that happens from Design Request page you can find Approve button, which finishes this process and creates a template in Template page which you can use in your campaigns.