Depends on whether you paid an estimated tax or you paid taxes with an extension request.

To enter, edit or delete estimated taxes paid (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 Estimates, click on the start or update button

Or enter estimates paid in the Search box located in the upper right of the online program screen. Click on Jump to estimates paid

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

I never asked for this to be done this year or any previous year.  I don't know why the amount was put there but it reduced my refund by half.

this is impossible since a payment can not reduce your refund. You can not enter a negative payment.  however, the usual place for entry is the payments worksheet.  another possibility is that you made a stray entry somewhere.

Do you mean the IRS reduced your refund by that amount?  If they did then there is nothing you can fix or amend.  You must have accidentally started an extension.  Or did you make an estimated payment and enter it on the wrong line?

Estimated payments should be on 1040 line 26.

An Extension payment is on line 31.