If you are using the TurboTax desktop editions installed on your personal computer all you need to do to start another tax return is to click on the File menu at the top left of the desktop program screen and click on New Tax Return.
If you used the TurboTax online editions then to start a new tax return you have to create a new User ID and password for the new user. Go to this TurboTax online editions website, choose the edition needed and create a new User ID - https://turbotax.intuit.com/personal-taxes/online/
