On the W-2 entry screen, the box 12 area will have two entry boxes: one for "code" and one for "amount." The code box will have a dropdown menu (click on right side of box) where you can select "D" from the options. Then just enter the figure in the amount box.
You can ignore the "16" after the D. It refers to a year (i.e. 2016) and doesn't get entered.
If you have additional codes & amounts, below the entry boxes you'll see a link for Add Another Row. You can add as many as you need. [edited 4/13/17]