After you file

Your second return will be rejected, you cannot e-file the same return twice.  You also cannot make changes to a return that has been filed. Since your first return was accepted to make any changes you would need to amend your return.  Amended returns must be mailed.

You need to put your first return back to the way it was when you filed. Then go through the amendment interview to make changes.  The IRS suggests you wait until your original return has been fully processed before you amend.