If you filled everything out in TurboTax Online after December 1, you filled out a 2020 tax return. There is no way to change it to an earlier year.
You cannot use TurboTax Online to file for a past year. TurboTax Online is only for the current tax year, which is now 2020. To file for an earlier year you have to use the CD or download TurboTax software for the year that you need. You can purchase a download at the following link.
Past Years' Products
You might get a better price from a reputable online seller that still has TurboTax in stock for the year that you need.
There is no way to transfer the information that you entered in TurboTax Online to a past-year tax return in the CD/Download software. You will have to start over in the CD/Download software. You should also clear the 2020 tax return that you filled out in TurboTax Online, so that the information you entered doesn't get mixed up with your 2020 information when you start your actual 2020 tax return.
Tax returns for past years cannot be e-filed. You will have to print your past-year tax return, sign it, and file it by mail. The IRS had stopped processing mailed tax returns for several months because of the Covid-19 pandemic. They recently started to process them again, but they have limited staff and a huge backlog, so it will be quite a while before your past-year tax return is processed.
TurboTax no longer supports years earlier than 2017. It's too late to get a refund for 2017 or earlier. You can file the tax return, but if it shows a refund you will not get the refund. If it shows a payment due, you have to pay it.
