Customers on Premium and Enterprise plans, with access to shipment plan validation, can print FNSKU item labels, formated for thermal label printers, instead of downloading the PDF from SellerCentral. The instructions for that are below.
Use the app printer settings to select your label size. You can access the settings by clicking on [Your name] at the top right drop down menu and selecting Account Settings. At the bottom of the page, click on Open Printer Settings.
From the popup dialog box, select the Item Label Size and if you want the Merchant SKU printed on the label.
From SellerCentral, download the shipment plan file, which contains the SKUs and item count that Amazon is expecting.
Access the Uploaded Shipment Plan page from the top navigation, Reports and selecting Plan Validation, and click on Print Item Labels for the shipment you want.
Apply the labels to your item. Here is a helpful video from Amazon on how to best apply the labels.