Open up AirPort Utility.....the application that you use to administer the TC. (Finder > Applications > Utilities > AirPort Utility)
Click on the picture of the TC
Click Edit in the smaller window that appears

Now, shift the focus of your eyes to the uppermost top of the Mac's screen.....up where you see the menus.....like File, Window, Edit, Help, etc.
Click on the Base Station menu
Click Add WPS Printer

There are two different WPS options to connect the printer, First Attempt and PIN. First Attempt is a substitute for a "button". PIN is used if your printer requires a code number.
Choose the option that is appropriate for your printer, and follow the prompts.