If you've instructed your employer to withhold extra money on your paychecks, that money will be included in your federal withholding on your W-2. You'll enter (or import) that information when entering your W-2 in the Income section of your interview.
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***
