You cannot use TurboTax Online to file for a prior year. TurboTax Online is only for the current tax year, which is now 2018. To file for a prior you have to use the CD or download TurboTax software for the year that you need. You can purchase a download at the following link. There is no free filing for past years.
http://turbotax.intuit.com/personal-taxes/past-years-products.jsp
You might get a better price from a reputable online seller that still has TurboTax in stock for the year that you need.
Tax returns for prior years cannot be e-filed. You will have to print your prior-year tax return, sign it, and file it by mail.