how can I go back and fix mistakes on state tax forms?

If you electronically filed and your state return was rejected, sign back in to TurboTax, then select Revisit or Fix it now.  If that doesn't work, see if the procedure in the TurboTax Help article What does my rejected return code mean and how do I fix it? helps you fix your rejected state return.

But if you're just talking about adjusting your state return information before filing, then, in TurboTax Online: 

1. Open TurboTax Online
2. Select  Tax Home in the left pane
3. Select the dropdown to the right of State Taxes
4. Select  Start, Review/Edit or Pick up where you left off
5. Proceed through the state interview

If the TurboTax Online navigation described above doesn't look like what you're seeing, see the TurboTax Help article Why does the TurboTax navigation menu look different for me?.

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