Please follow the Shopify label printing video at YouTube:
Or follow these simple steps to setup your Shopify to Print to ITPP941.
Click on Settings on the left hand side menu.
Choose Shipping under Settings.
Set your Shipping Label Printing to "4 x 6 label printers (DYMO or similar). Click on "Print test label" to print a sample label to your ITPP941.
Alternatively, you may update your label settings when you are purchasing postage for your order. Please refer to the screenshot below.