The Purchase Order Preferences screen can be accessed from your dashboard by clicking on the vertical ellipsis (⋮) on your Purchase Orders App and selecting Preferences.
When a purchase order is created, you are given the option to print the purchase order.
This screen allows you to choose the purchase order template that will be used.
Select it from the dropdown and click Save & Back.
If you want to make changes to the print template, you can only do so in Report Designer.