To clarify, reported the nondeductible traditional IRA contribution for 2023 on Form 8606 but you didn't make the contribution by April 15th, 2024?
If yes, then you will have to file a corrected 2023 Form 8606. Please see How do I amend my federal tax return for this year? If there are no other changes on your return then you can file the corrected Form 8606 by itself and mail it to your designated IRS office. Be sure to include your address on page 1 of the form and your signature and the date on page 2 of the form.
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