The Form W-2 must be entered as received, including the code-W entry. The entire amount contributed to your HSA via your employer, reported with code W in box 12 of your W-2, has already been excluded by your employer from the amount in box 1 of your W-2. You do not get to deduct it again. Do not enter any of this amount as a personal HSA contribution. Personal HSA contributions are those you make directly with the HSA without any involvement of your employer.
