Did you use the Online version or the Desktop program? Are you sure you were looking at the 2023 and not 2022 return? And when he said "not possible" was he considering his income minus things like 401k contributions? The wages in box 1 might be a lot less than his gross wages. Also what "gross income" did you give him? Wages on1040 line 1 or the AGI on line 11 or taxable income on line 15?
Oh you said Desktop? Did you use Desktop for both years? Have you actually printed out both 2023 & 2022 and compared them? Maybe you have more than 1 2023 return? When you go up to File - Open is there another return? Your tax data files end in .tax2022 and .tax2023. In Windows they should be in your Documents in a Turbo Tax folder.
Before you amend you should get a transcript from the IRS and see what was filed. Request a transcript from the IRS
https://www.irs.gov/individuals/get-transcript
