If you have used the desktop version of TurboTax, you have up to 5 returns. From the File menu at the top, go to New Tax Return.
If you are using TurboTax Online, each return will need a separate account with a unique username/email.
You can find the instructions here: https://ttlc.intuit.com/questions/3495821-need-to-create-a-new-account
