The Estimated Federal Tax screen specially says "Don't enter... any 2023 overpayment applied to this year's return." So where DO I enter it? Multiple calls with customer service and no answer. Other than maybe form 1040X. But they can't find that either.
You do NOT have to use a 1040X to use your 2023 overpayment (refund) balance that you chose to apply to your 2024 taxes.
Assuming you haven't yet filed your 2024 return, here's how to enter your 2023 overpayment (refund) which you applied to 2024 taxes. If you used TurboTax in the same account as last year, it might already show up there, but you need to check and be sure, and enter it if necessary.
I assume you're using Online TurboTax. Below are 2 different ways to get to the right place:
Open your return interview and in the left menu column:
Or here's a shortcut you may be able to use for a faster way: