This is referring to the WPS (WiFi Protected Setup) PIN. To find the PIN, do the following.
Log in to the TEW-671BR by entering https://192.168.10.1 into the address line of your browser.
You will be prompted to log in to the Router. The default username and password are both admin.
After you have logged in to the Router click on the Wireless 2.4GHz or Wireless 5GHz > WPS page. The PIN is listed as the Self PIN code.