For starters, the online version of TTX can only be used for the current tax year, which right now is 2017 until October of 2018. TurboTax online for the 2016 tax year is shutdown and gone permanently and forever. Additionally, your extension expired in October of 2017. However, if what you paid with your extension was paid prior to Apr 17th, 2017, and if what you paid covers your 2016 tax liability in it's entirety, then no late filing penalties or late payment penalties will be assessed when you do file your 2016 tax return.
Apparently, I did not save a copy of anything.
You now get the thrill of starting over from scratch. That means you'll have nothing imported from your .tax2015 tax file. Now you can download your .tax2016 file from your online account, but you will first have to pay your online 2017 TTX fees to access it. That creates yet another hassle when you go to file your 2017 taxes with the online version, because you have to jump through hoops of fire to transfer the data from your .tax2016 file on your desktop, to your 2017 tax file online.
So lets deal with filing the 2016 return for now, and don't worry about your 2017 tax return until that is done in it's entirety. Otherwise, you'll just add to your own confusion.
To access your .tax2016 file online, you'll have to purchase PLUS or higher. Access instructions for prior year's returns are at https://ttlc.intuit.com/questions/3404575-how-do-i-access-my-prior-year-2016-return