Did the IRS change your refund or tax due? If you agree with it then you do not need to amend. Was line 31 for a payment made with an extension? Or for what from Schedule 3?
The amount you paid with the extension (or you put down on the extension that you would pay) shows up on 1040 Schedule 3 line 10 which goes to 1040 line 31. If you didn't pay it with the extension then you need to delete the amount.
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