If you have a printer that is physically attached to one computer, and you have Smartprint installed on another computer, then you need to tell Windows to both share the printer and make it visible.
Click the start menu and type in control, then click Control Panel from the suggestions list.
Depending on your set up, you will see something that looks like this:
or
If it looks like the first image, click View devices and printers, which can be found under the Hardware and Sound category. If it looks like the second image, click Devices and Printers.
Right click the printer to share, and click Printer properties.
(Note that here, we are using the generic printer as an example. Yours will be the name of the label printer, for example Zebra GK420d. App printers will have the same menus)
Click the sharing Tab.
Tick the Share this printer checkbox, and give it a name, something like LabelPrinter or LabelPrinter01. Note that this name is unrelated to the Printer's own name. Please don't use spaces or symbols as this can cause problems.
And Click OK.
With the printer shared, we now need to tell Windows to let the PI connect.
To do this, click the up arrow next to the address bar
Click Network and Sharing Center (your icons may be smaller than the ones in this image)
Click Change advanced sharing settings, which can be found on the left.
It gets a little trickier here.
This is split into sections, usually named things like "Private" and "Home or Work" and "Guest" or "Public".
Every section needs to be expanded in turn, then network discovery and file and printer sharing set to on and password protected sharing set to off. Any other settings can be left as-is
Finally, click Save changes.