Form W-2C, Corrected Wage and Tax Statement is issued by an employer when a mistake is discovered on Form W-2. In TaxAct, you enter your wage information the same way, whether you receive Form W-2 or Form W-2C.
See Entering in Program - Form W-2
If you receive the W-2C after you have submitted your return to the IRS (and it has been accepted) then you will need to amend your return.