Yes, as long as you haven't mailed the return (or e-filed) in yet then you can make changes, please follow these instructions:
- In TurboTax Online, sign into your account.
- Select Tax Home in the left menu.
- Scroll down to Your tax returns & documents.
- Select 2018, and then select Add a State (you're not actually adding a state, this is to open it back up)
- Make changes and then file
