if you were married on 12/31/2020, single was not a valid filing status for either of you (at best two married filing separately returns or if you lived apart for the last 6 months of the year and one maintained a household for a dependent for the last 6 months of the year that person could file as head of household while the other would use married filing separately). to file jointly, assuming neither of you was not a US resident or citizen. then you need to select one of those returns for amending. Then you would need to enter the other spouse's info including income and deductions and change filing status to filing jointly. the other return does not need to be amended. The return must be filed by 5/17/2024 to claim any refund., it cannot be efiled.
How do I amend my federal tax return for a prior year? (intuit.com)
if you used online you may need to purchase the desktop version for 2020 to amend.
