On form 1040 where to enter $3,700.00 for additional taxes mailed with my extension request

[xmasbaby0]

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 

[VolvoGirl]

If you made a payment with the extension,

For 2019, If your extension payment did not automatically show up on 1040 Schedule 3 line 10 which goes to 1040 line 18d you need to enter it. So make sure it's not already there before you enter it!

You can type estimates paid in the search box at the top of your return and click Find and it will give you a link to Jump To the screen where you enter Extension Payments.

To enter the amount you paid with an extension (including state extension) go to

Federal Taxes (or Personal for desktop H&B version)

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