After you file

If your return has been transmitted and rejected by the IRS, you can correct your tax return and re-transmit.

If your return has been transmitted and accepted by the IRS, you will have to amend your Federal 1040 tax return.  However, before amending your tax return, do not enter the return and do not make any changes.

If your return has been transmitted and accepted by the IRS, you will not be able to electronically file a second tax return with another service. 

Amended tax returns will not be available before February 13. See forms availability here.

If you used TurboTax Online, log in to your account and select Amend a return that was filed and accepted.

If you used the CD/download product, sign back into your return and select Amend a filed return. 

See also this TurboTax Help.

In the amended tax return, go to My Info.  Select the box next to Another taxpayer can claim me as a dependent on their tax return.