If you filed the extension (Form 4868) from within TurboTax, the amount of your payment should be automatically entered in your tax return. It should be on Schedule 3, line 9. If it's not there you have to enter it yourself.
To enter the payment you made with your extension, type "estimated tax payments" (without the quotes) in the Search box, then click the link that says "Jump to estimated tax payments." That takes you to the screen that says "Estimates and Other Income Taxes Paid." Scroll down a little to the second section, "Payments with Extension." Click the Start, Update, or Revisit button for payment with 2020 federal, state, or local extension, as appropriate.