You can download the box contents by selecting the shipment and pressing the "Download Pack List" button in the purple toolbar and upload that to Amazon. In order to upload to Seller Central, you'll need to change the background color of the column between the "Boxed QTY" and "Box 1 - QTY" columns and the row before the "Plan ID:" row to an arbitrary color as demonstrated in the image below. This is required by Amazon's upload process.