After you file

When you make an estimated tax payment, it will show on line 26 of form 1040 "Estimates and other taxes paid" regardless of where you enter the estimated payment in TurboTax. However, there is a place to enter it in TurboTax, for which you need to choose the Visit All tab in the Estimates and other Taxes Paid tab as follows:

Then, you will come to a screen that says "Federal estimated taxes for (year)  You can enter your estimated tax payment there.