It depends.
If your return was not accepted, you can simply log back into the program and make your changes and try re-filing it again.
If your tax return has been filed and accepted, you will have to file an amended return to make the correction.
Please see the following link for instructions on whether you actually need to file an amended return and if so, steps on how to prepare the amended return.
Do I need to amend?
How to amend my return