When amending in TurboTax you'll revisit the HSA contribution section, indicate that you were covered by Medicare for October, November and December, then, when TurboTax indicates that you made an excess contribution, indicate that you will have the excess returned. TurboTax will prepare Form 8889 with the correction to the contribution amount and Form 1040-X showing an increase in taxable income equal to the amount of the excess. At the top of the Form 1040-X you'll need to write "Filed Pursuant to section 301.9100-2."
The code-2 2024 Form 1099-SA showing the amount of attributable taxable gains that accompany the distribution of the excess will be reportable on your 2024 tax return, not on your 2023 tax return.
