Yes, you can still file a 2016 return, but not in Online TurboTax. You have to use 2016 desktop software (CD/download) to prepare the return.
The 2016 return has to be printed, signed, and mailed. It cannot be efiled.
You can purchase the 2016 software as a download directly from TurboTax at the link below, or you may be able to find it at a discount at a
reputable authorized retailer like Amazon, etc.
https://turbotax.intuit.com/personal-taxes/past-years-products/If puchasing elsewhere, be aware that Deluxe Edition comes in 2 versions--one that is Federal only, and one that is combo Fed and State. When purchased from TurboTax, it is the combo version. When purchased elsewhere, you have to be careful as to which Deluxe version you are buying.
Or are you asking how to finish a 2016 return you started online? If so, see this:
https://ttlc.intuit.com/questions/2559403-how-do-i-finish-a-prior-year-return-that-i-started-in-turb...
