You cannot file a tax return for free right now. E-filing for 2016 is closed. You must use desktop software to complete the 2016 filing process; the lowest version available is Deluxe. (And you cannot file for 2017 yet. The online software is not yet available for 2017).
To finish a prior year return started in TT online:https://ttlc.intuit.com/questions/2559403-how-do-i-finish-a-prior-year-return-that-i-started-in-turb
Your return will have to be printed, signed and mailed,