you will see a “Featured Image” box in the new pano post area, you can drag this box (or any other) by its title bar to a different position if it is hidden below other boxes

click on the “add featured image” link in this box and drop an appropriately sized jpg image (dimensions must be 1600 px x 800 px, file size less than about 400kb) onto the resulting upload window

drop your image on this upload area, once it is uploaded (should be very quick) make sure it is selected and then click the “Set Featured Image Button”
sam