You file one tax return that lists all your income, deductions and credits.
At this point, you need to wait for your tax return to be processed and any refund to be paid. Then you file an amended return to correct the missing information. If you owe a tax payment (because your new calculated refund is smaller than the amount you were paid), you need to pay that by April 18 to avoid interest charges.
Turbotax usually turns the amending function on in late February or early March.
