Or actually do not pay it now but just pay the final tax due on your tax return when you file. If you don't pay a separate payment now then make sure to delete the estimated payment from your tax return so it is included in any tax due. You don't want to get credit for it if you haven't paid it.
To enter or delete the amount paid with an extension go to
Federal Taxes (or Personal for Home&Business)
Deductions and Credits
Then scroll way down to Estimates and Other Taxes Paid
Income Taxes Paid - Click the Start or Update button
Next page second section Payments with Extension
Either Visit All or Click Start or Update by the extension you paid or didn't pay