D-Link DWA-556 User Manual page 21

Section 3 - Configuration
If you want to connect using the PBC method, refer to page 14. To use
the PIN method, select PIN (Personal Identification Number) and click
Next.
Click Next
Make sure your access point or wireless router is close by. Write down the
number on the screen. Enter this number in your access point or wireless
router. Please refer to the manufacture's manual for instructions.
Once you click Next, you will have 2 minutes to enter this number in
your access point or wireless router.
Click Next
D-Link DWA-556 User Manual
Personal Identification Number (PIN)
21