How do we enter an estimated tax payment made from our 2023 overpayment (via the 1040-SR line 36, not via the 1040-ES form)?

Here is how you can indicate you applied your 2023 federal overpayment to 2024 in TurboTax Online:

1. Navigate to  Federal > Deductions & Credits > Estimates and Other Taxes Paid  > Start or Revisit
2.  On the Income Taxes Paid screen, choose 2023 Refund Applied to 2024  federal taxes > Start or Revisit
3. Enter the amount