If you purchased 2016 software in 2018 it would have to be desktop software that you could download to your own PC or Mac. You say "I did my taxes..." Then if you used the desktop software that you downloaded the tax file has to be on your own hard drive. Returns prepared using desktop software are not stored online. They are stored on your hard drive or any backup device that you used like a flash drive.
https://ttlc.intuit.com/questions/1901659-find-your-tax-data-file-in-mac
https://ttlc.intuit.com/questions/1900721-find-your-tax-data-file-tax-file-in-windows
The only way for you to file a 2016 return is to print, sign and mail it. It is now too late to receive a refund for a 2016 tax return even if one is shown on the return. You forfeited the refund as of July 15, 2020. But if you have tax due, you still have to pay it.
If you are getting a refund, there is not a penalty for filing past the deadline. If you owe taxes, the interest/penalties will be calculated by the IRS based on how much you owe and when they receive your return and payment. The IRS will bill you for this; it will not be calculated by TurboTax.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
