See this TurboTax support FAQ for completing a prior year tax return started with the online editions - https://ttlc.intuit.com/questions/2559403-how-do-i-finish-a-prior-year-return-that-i-started-in-turb...
Tax Year 2016 Important Dates -
October 16, 2017
- Final deadline to file your 2016 personal tax return if you filed an extension.
October 21, 2017
- Final deadline to resubmit a rejected return that was originally e-filed on or before October 16.
- If you're expecting a refund and miss the October 21 final cutoff date, you have until April 15, 2020 (October 15, 2020 if you filed an extension) to file a paper return and claim your 2016 refund.