Did you file a 2018 federal return using TurboTax? If you did not, then you cannot use TurboTax to prepare a "stand alone" state tax return. Information flows from the federal return to the state return with this software. If you used TurboTax to prepare a 2018 federal return then you can access the account you used and then you will have to download the CD/download software for 2018 to a full PC or Mac in order to complete the 2018 state return.
You have to access your own account and/or print it for yourself using exactly the same account and user ID that you used when you prepared the return.
Many people have multiple TT accounts and forget how to access them. Log out of the account you are in now.
Account recovery
https://myturbotax.intuit.com/account-recovery/
https://ttlc.intuit.com/questions/1901535-forgot-your-turbotax-online-user-id-or-password
Or did you use the desktop version of TurboTax? If so, the files are on your own hard drive or any backup device you used like a flash drive.
https://ttlc.intuit.com/questions/1901486-how-many-turbotax-accounts-do-i-have
https://ttlc.intuit.com/questions/1900990-how-do-i-file-a-prior-year-tax-return
Another way to do it would be to go to the state's tax site and get the 2018 forms to prepare and mail in. You will need information from your 2018 federal return.