You have to start over from the beginning.
If using online, with your return open click My Account at the top right, then select the option to clear and start over. If you have already paid for your return, then the clear and start over option is not available.
If using the desktop version of the program you physically installed on your computer, close the program and delete your tax file in the documents\turbotax directory. You tax file will have a filename extension of .tax2016
