Where do I input the 2023 Illinois overpayment carryforward in the 2024 Turbo tax

If it didn't transfer over from last year then enter a refund from last year that you applied to this year here.   BUT first make sure it's not already there.  You don't want to apply it twice.

To enter last year's refund you applied to this year.

Federal (Personal for Home & Business)

Deductions and Credits

Then scroll way down to Estimates and Other Taxes Paid

Other Income Taxes - Click the Start or Revisit

Next page scroll down to 2023 Refund Applied to 2024

Click Start or Update by the tax you applied

Then for state, you need to click on the state tab and go through state again for it to update.