To enter contributions to an HSA:

Select Federal Taxes
Scroll down and select Show More at Less Common Income
Select Start or Revisit at 1099-SA, HSA, MSA

Go through the screens in this section. Respond yes to "Did ___________ put money into an HSA in 2016?". Over the next 3 screens you will put in information about your employers contributions that were not reported in Box 12 of your W-2.