See the instructions in the TurboTax FAQ below for beginning a second return in TurboTax Online.
"How do I start another return in TurboTax Online?"
https://ttlc.intuit.com/replies/3288574
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***