Will need to file an amended return. I have already deleted the TurboTax program

I have filed and received my refund. My employer has just informed us that they made an error on our W2's for what amounts to a few weeks of salary.

We will be receiving amended W2's.

I have already removed the Turbo Tax program from my computer. ( I have the saved files of course).

Do I just re install the program to access my return to do the amended return. Also is the filing of the amended return free, or should I be sending the bill to my employer.