I'll include instructions for fixing your mistake below. Depending on what your mistake was, it can be better to delete the state and add it back. While this can take a few extra minutes, it can save time in the long run.

To make changes to your state: 

1. When you login, click Take me to my return
2. Next, select the State Taxes tab and then Continue.
3. On the state tax summary page, you'll see your state tax return(s) listed. Click the Edit button next to the state and you'll be able to review your state entries and make changes. If you're unable to find the questions to change or you don't get the desired affect, then you'll need to delete (next to Edit) the state and adding it back by clicking + Add another state.