You will need to follow the steps below to finish that 2016 return. It cannot be done online. TurboTax Online is only for the current tax year of 2017.
And the 2016 return would then need to be printed and mailed. You cannot e-file a prior year return.
This link
How do I fix a rejected return? will walk you through steps of fixing a rejected return, so that you can fix it when you go to print and mail it.
When you mail the return, be sure to attach any documents showing tax withholdings (i.e. W-2’s and 1099’s). You may also want to use a mailing service that will track it, such as UPS or certified mail so you will know the IRS received the return.
How do I finish a prior-year return that I started in TurboTax Online?
