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.
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.
No you cannot change the year. The online program is ONLY for 2020 returns -- no other year and there is no way to change it. If you put data for the wrong year in, clear it out and save the account for your 2020 return.
CLEAR AND START OVER
Online preparation and e-filing for 2017, 2018 and 2019 is permanently closed.
To file a return for a prior tax year
If you need to prepare a return for 2017, 2018, or 2019 you can purchase and download desktop software to do it, then print, sign, and mail the return(s)
You may also want to explore purchasing the software from various retailers such as Amazon, Costco, Best Buy, Walmart, Sam’s, etc.
Remember to prepare your state return as well—if you live in a state that has a state income tax.
When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.
Federal and state returns must be in separate envelopes and they are mailed to different addresses. Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.
Note: The desktop software you need to prepare the prior year return must be installed/downloaded to a full PC or Mac. It cannot be used on a mobile device.
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.