The IRS already knows that you filed an extension request.  There is nowhere on the tax return to indicate an extension was filed nor is there a need to indicate an extension was filed.

If you paid any taxes with the extension request, the taxes paid have to be entered on your tax return.

To enter, change or delete a payment made with an extension request (Federal, State, Local) -

• Click on Federal Taxes (Personal using Home and Business)
• Click on Deductions and Credits
• Click on I'll choose what I work on (if shown)
• Scroll down to Estimates and Other Taxes Paid
• On Income Taxes Paid, click on the start or update button

On the next screen select the type of extension payment made and click on the start or update button

Or enter federal extension payment in the Search box located in the upper right of the program screen. Click on Jump to federal extension payment

The federal extension payment will be shown on Schedule 3 Line 9. The amount from Schedule 3 Part II Line 13 flows to Form 1040 Line 31

"There is nowhere on the tax return to indicate an extension"

When you enter an amount on the relevant line, Schedule 3 line 9, , that would pretty much do it.

Generally, you don't need to file an extension request if you don't owe tax on April 15.