When the printer options window is opened, it will present any available PriceTag® printers installed on the system.
Just select the printer you want to use from the list view and click on OK to confirm.
If you want to use the selected printer for all loaded card-templates, make sure you leave the option checked for "Apply these settings to all loaded cards" otherwise each card-template will have it's own specific printer connected. By default this is always checked as it is likely you will only have one PriceTag® printer connected.