If you are using the Online version sign into your account with the same UserID & Password you used to start your return.

If you cannot get back into your return, see the following

1.      In TurboTax Online, sign into your account.

2.      Select Tax Home in the left menu.

3.      Scroll down to Your tax returns & documents.

4.      Select 2018, and then select Add a State (you're not actually adding a state, this just opens the return back up)

5.      Make changes and then refile