Each TT online account is good for only one Federal and related state income tax returns. To prepare another, you will have to open a new account with a unique name and password. Persons who need to prepare more than one return, and especially when a state return is involved, are usually better served by the CD/Download version of TT that allows you to prepare as many Federal returns as you need and, with versions Deluxe and above, includes one free state return preparation program.
The Online version is only good for 1 return. But you can use the same email address for 5 accounts. To do another return you have to set up a new account and new user name and pay any fees again. So if you have more than 1 return to do it might be better to buy the Desktop program. And Desktop has more features.
How to start another return in the Online version