As long as your return is still in progress, you can go back and add an additional W-2 to your return

• Login to your TurboTax Online Account
• In your tax timeline, click Take Me To My Return
• Click Federal Taxes < Wages & Income < Edit/Add or Start (if you have not added a W2)
• Enter the information from the W2

If your return has already been efiled and accepted, you will not be able to add the W-2 to your original return. You will need to complete an amended return in order to add the W-2