Use Form 1040-X to add or correct information on an already filed Tax return.
If you e-Filed 1040 and got ACCEPTED, it is still possible to e-File 1040-X.
Make sure it is all correct before submitting 1040-X
If it was perpared for mailing before you paid some wrong "amount you owe", it probably is missing that infomation.
@lovingdead
