I got a letter from IRS in 2021 saying we have adjusted your taxes and you need to make a payment ($475.00). I did. Have lost the notice. Where do I enter it for 2021?

You do not enter anywhere on your 2021 federal tax return that you paid your federal tax from a previous year.   It is not deductible.

There are six states that allow you to enter the federal tax you paid on your state return--Alabama, Iowa. Louisiana, Missouri, Montana, and Oregon.  If you are filing in one of these states watch for the deduction when you prepare your state return.

Does TT not need to know I made an extra payment for the previous year taxes when it imports data to work on this years taxes?

Or does that not matter, or have any effect on this years tax filing.

It has no effect on your 2021 return.