Follow these simple steps to setup your Shopify to Print to Rollo.
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 Rollo.
Alternatively, you may update your label settings when you are purchasing postage for your order. Please refer to the screenshot below.