My W-2c has

previously reported

federal income tax withheld

(blank)

and then

correct information

federal income tax withheld

(blank)

however on the original W-2 it has an amount listed for federal income tax withheld.

what should I do when I file?

Is there anything else on your corrected W2 (W2C) not on your original W2?  

If you already entered your W-2 and you haven't yet filed, go back and edit your W-2 with the corrected info from your W-2c.

I had already filed with my original W-2 before seeing my employer had also uploaded a W-2C. The only things corrected on the W2-C are the following fields:

Wages, tips, other compensation

social security wages

medicare wages and tips

social security tax withheld

medicare tax withheld

the rest is all blank from boxes 2 (federal income tax withheld - both for "previously reported" and "correct information")

and boxes 7-20 (including all state information is blank).

If your return has already been accepted, then you will need to amend your return.  If it gets rejected, then simply log back in and make the corrections to your W2.

You should wait until your original return is fully processed before you amend (you receive a refund or pay balance due, if applicable).

If you prepared your original tax return using TurboTax:

1. Log in to your account.
2. Open the tax return you already filed.
3. Click on the link to amend your return.
4. The software will walk you through the process of filing the amendment.

If you amend your federal return, the changes will automatically be transferred to your state tax return.  

TurboTax FAQ: How do I amend  my state tax return?

@azrebiec