Entered incorrect amount for $ paid at the time of extension - how to fix it?

When you requested your extension you were supposed to pay your estimated tax due.  Did you enter the payment you made into your tax return?  Go to Federal>Deductions and Credits>Estimates and Other Taxes Paid>Other Income Taxes 

Did you already file the tax return with the incorrect payment amount, or are you trying to correct it in TurboTax before you file?

If you have not yet filed, following the instructions that xmasbaby0 gave you above to go to where the payment is entered and change the amount.

If you have already filed, wait and see what happens when the IRS processes your tax return. They may correct the error for you, without your having to do anything. They know how much you actually paid. If the IRS does not correct it, you will have to file an amended return.