TurboTax online for 2016 is now closed, and 2016 is considered a prior-year return. You will need to purchase the 2016 software, download and install it on your computer, and prepare your return. You'll also need to print and mail your 2016 return, as prior-year returns cannot be e-filed. The info in the TurboTax FAQ below will instruct you on how to proceed.
https://ttlc.intuit.com/replies/5546147
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***