Amend 2021 return after receiving CP23 notice

[joe56ny]

After I filed using Turbo Tax 2021 Home & Business, I received a CP23 notice saying I owed $3700 due to an error on my Recovery Rebate Credit.  I have paid the balance due, and now want to amend my return to add an elderly family member as dependent (I had previously done this in 2020 but forgot to add her in 2021).  Where do I enter the balance due payment that I made when I amend my return?  I see no option in "Personal - Deductions & Credits" that applies to additional federal taxes paid for 2021.  

[fanfare · Accepted solution]

put the amount  you've paid IRS so far on 1040-X line 16.

not estimated tax and not withholding which goes elsewhere