If you have not yet e-filed the tax return by completing all 3 Steps in the File section of the program and clicking on the large Orange buton labeled Transmit my returns now then just delete the W-2's you entered.
After completing the File section and e-filing your tax return you will receive two emails from TurboTax. The first email when your tax return was transmitted and the second email when the tax return has either been accepted or rejected.
If you did e-file the return, then there is nothing you can do. Once the return is e-filed it cannot be retrieved or canceled. Once the IRS starts accepting 2019 tax return on January 27, 2020 you may get lucky and the tax return will be rejected. Then you can make the correction and re-file. If the return is Accepted you would then have to file an amended tax return to make the correction. An amended tax return can only be printed and mailed. It will take the IRS about 4 months to process the amended tax return.