you first have to split the shipments up into how ever many...
after you do that, when you click on the order number, you will get a screen, where on the top right there are X number of shipments. Click on any of those to enter individual info.
when you click on your order, underneath items, there is an "S". clicking on that will split the shipments. Thing is, is I'm not sure how to recombine the shipments afterwards...