How do I determine how much estimated taxes to pay in 2025 using ttax24 if my income will be unever due to e.g. Roth conversions

Here is how to update in TurboTax Online:

1. Navigate to Federal Taxes > Other Tax Situations
2.  Go to Other Tax Forms
3.  Start or Revisit Form W-4 and Estimated Taxes
4. Continue past the W-4 section to get the estimated tax section, Estimated Taxes for 2025 
5. You will be asked if you want to adjust  your income or deductions, answer yes, and here you can enter your predictions including the Roth conversion.