Navigate to the Snapshot link. Click the "Enter" button to go to the "Take a Selfie!" page. In the url bar at the top of the page, you should see a camera icon. Click on the icon. A new popup menu should appear, click on the "Manage" button.

This should have opened Chrome's Camera settings in a new window. Near the top of the page, there should be a grey dropdown button. If you click this area, a list of all your connected cameras* will show up.

☝ ** If the camera you looking for is not in here. please restart Chrome and try this again.

Select the camera you're interested in. Now go back to the Snapshot tab. Refresh the page, and navigate back to the "Take a Selfie" page. You should now be using the external camera.