Unfortunately, the IRS agent provided you the wrong advice.
See: IRS Amended Return Frequently Asked Questions which includes this question and answer:
What are some reasons that an Amended Return cannot be filed electronically?
Amended Returns must be filed by paper for the following reasons:
- Only Tax Year 2019 and 2020 1040 and 1040-SR returns can be amended electronically at this time. Amended Returns for any other tax years or tax types must be filed by paper.
- There must be a record of an "original" electronically filed return for Tax Year 2019 or Tax Year 2020. If the original Tax Year 2019 or Tax Year 2020 return was filed by paper, it must be amended by paper.
- If the Primary Social Security number is different from the one provided on the Original Return, then the Amended Return must be filed by paper.
- If the Spouse's Social Security number (if applicable) is different from the one provided on the Original Return, then the Amended Return must be filed by paper.
- If the Filing Status differs from the Filing Status on the Original Return, then the Amended Return must be filed by paper.
Secondly, if TurboTax is changing your filing status from Head of Household to Single, then there may be an issue with whether your situation meets the rules to claim Head of Household. For more information, see: Do I qualify for Head of Household in 2020.
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