Were you married before the end of 2020? If not, you cannot file as married filing jointly for 2020.
If you do want to change your filing status, you have to file an amended return (Form 1040-X). You choose one of your single tax returns to amend. In the amended return change the filing status to married filing jointly, and add all of the other person's information and income. The other single return, that you do not amend, will simply be disregarded. You don't do anything with it.
If your amended return will result in an additional refund, you must file it by this Friday, May 17, in order to get the refund. If you file it after May 17 you will not get the refund.
See the following FAQ for instructions to amend a tax return that you filed with TurboTax.
How do I amend my federal tax return for a prior year?
You cannot e-file the amended return. It has to be printed, signed by both of you, and filed by mail. To get a refund it must be postmarked by May 17. It is currently taking 20 weeks or more for the IRS to process an amended return.
Amending a return to change the filing status can be complicated, and you have a tight deadline. You might want to go to a local tax professional for help.
