No new or corrected forms will be issued for 2023.
When amending, in TurboTax you'll just revisit the HSA section, indicate Medicare coverage for October through December, then indicate that you'll remove the excess (which you will already have done by October 15, 2024). You must also indicate at the top of the Form 1040-X that it is being "Filed pursuant to section 301.9100-2." The excess will be added to income, so you'll owe the tax due to the increase in taxable income. Line 9 of the 2023 Form 8889 will change to show the lower employer contribution, reduced by the amount of the excess that will be added as income.
Investment gains required to be distributed along with the excess will be taxable on your 2024 tax return.
