Yes, you should file an amended return if your Federal withholdings were listed incorrectly on your tax return.  Here is how:

In order to file an amended return, make sure that your 2019 return was accepted in TurboTax Online or paper-filed through the mail by the IRS.

To prepare an amended return through TurboTax, follow these steps:

1. Sign in to TurboTax.
2. Scroll down to Your tax return & documents (you may need to select Show), select 2019 and then Amend (change) return.
3. Select Amend using TurboTax Online.
4. Carefully follow the instructions. Don't worry if your refund changes to $0. This is normal on amended returns.
5. When finished, we'll give you instructions for printing and mailing your amended return as amendments can't be e-filed.

I used Turbo Tax from a CD.  I try opening a form 1040X for my accepted 2019 return, but no information populates it - no personal info, filing status, numbers from my original 1040.  I somehow put all of my est tax payments and withholding on the withholding line.  (I'm not sure how I did that in the first place.) I need to separate them for the amended return. So I really have to reenter the whole return?  Thanks.