After trying to resolve this same issue with Form 2210 in the Online version I spoke with TurboTax representative Dana. I informed her I was trying to just go to the form directly and change the uncooperative inputs. She suggested using the desktop version, which is the old TurboTax version I was familiar with. Next year I'm going back to the desktop version. Was able to go directly to the forms and update the withholding amounts correctly.
