First, if you have Net Operating Loss Carryforward amounts from 2015 that would have affected your taxable income for 2016, you need to file an amended return to include the NOL for 2016. See How to Amend (Change or Correct) a Return You Already Filed.
However, if you had an NOL from 2016, you may need to enter the amount of the net operating loss carryforward on your current return.
The easiest way to find this section of TurboTax is to use the Search box at the top right side of the TurboTax header. Click on the magnifying glass, type in "nol carryforward", hit Enter, and click on "jump to nol carryforward" to go directly to beginning of this topic.
Or go to My Account >> Tools >> Topic Search. Type in "nol carryforward", then click the topic in the list to go directly to the start of this section.
(If you are using the mobile app and don't have My Account or Tools on your screen, try logging into TurboTax from a laptop or desktop browser.)
If you used TurboTax last year, there may already be an entry for the NOL carryforward. Otherwise, enter the NOL as a positive number.
Note that a Net Operating Loss appears on Form 1040, Line 41.
If you used TurboTax last year, any net operating loss available to carry forward is shown on "Carryover Wks" Line 14a. This is a TurboTax worksheet, not an IRS form.