How do I add a 1099INT

Please clarify - is this interest paid to you by the IRS or is this bank interest that was paid to you that the IRS told you about?

Either way it sounds like you need to amend your 2024 tax return and add a 1099-INT.  Log in to your TurboTax account and go to the 2024 tax return (or whichever year this letter refers to).  Then click on the button that says 'Amend this return'.  Then you can add the 1099-INT.

If the 1099-INT is something that is referred to in a letter from the IRS then the bank that sent it to you should be on the second or third page.  That will help you to enter it.

@spmichaeltazzz