Well... you can't ensure this automatically, there is no box to check...To carry back NOL means that you must amend your prior year tax returns and report NOL. You must go back two years before the NOL year...For example, if you incurred NOL in 2016, you must first amend your 2014 tax return and report your NOL on 2014 tax return, Then, if you still have some NOL left, you must amend your 2015 and enter the remaining amount of NOL on 2015 taxes. Then, whatever is left is carried forward to your future years.
IRS offers two options or reporting carry back your NOL. One is as I explained above, the second option is to just file Form 1045. That form is not supported by TurboTax due to the complexity of the NOL, but you can print the form from the IRS website and file it by itself. The form 1045 is not attached to the return; it must be mailed separately.
Here are links to the Form 1045 and its instructions, if you prefer to file the form instead of amending the prior years:
https://www.irs.gov/pub/irs-pdf/f1045.pdf
https://www.irs.gov/pub/irs-pdf/i1045.pdf
And more information on the NOL itself:
https://www.irs.gov/pub/irs-pdf/p536.pdf
