Hi and welcome to our site!If the person incorrectly used "married filing separately" filing status - yes - the error may be corrected and the tax return could be amended with changing the filing status to "single" or another appropriate status.To amend - use form 1040X - and provide explanation.No supporting documents are needed unless the IRS specifically requests.
Would you therefore agree or disagree with this JustAnswer provided by RD:
If you filed separately on original tax return than you can amend and change a return to married filing jointly. You can't, however, do the reverse. Changing from joint to separate filing after a return's deadline is past is not allowed. You will only file one Form 1040X.
That statement is correct. But the limitation is related ONLY to change from "married filing jointly" to "married filing separately" - and it is assumed there is no error in selecting the filing status.
So the first step would be to verify which filing status may be used by that person? If "single" is allowed for that person? That determination generally must be made on the last day of the tax year.