The answer depends on whether or not your error in reporting the basis on your 2016 tax return affected the taxable amount of any 2016 traditional IRA distributions or Roth conversions. If it did, you must file an amended 2016 Form 8606 along with Form 1040X. Even if you did not have any traditional IRA contributions or Roth conversions in 2016, filing an amended 2016 Form 8606 with Form 1040X would be the most proper way to make the correction since it explicitly shows that your 2016 tax liability is unaffected.
If you file a corrected 2016 Form 8606, you would then provide to TurboTax as your basis carried in from 2016 the correct amount from line 14 of the amended 2016 Form 8606 and not provide any explanation for basis adjustment with your 2017 tax return.
If you do provide an explanation with your 2017 tax return, it will be included in your filing.
