Instead of mailing a paper check, you already paid your CA income taxes using ACI payments, there is nothing else to change or do. You don't have to mail a paper check even if you selected a paper check within TurboTax. How you decide to pay your CA income tax is between you and CA.
No, once you have filed your return and it is accepted you can not change the payment method selected when you filed your return.
Ok thanks. What should I do if I already went ahead and paid my state tax online through ACI even though I selected mail check?
Instead of mailing a paper check, you already paid your CA income taxes using ACI payments, there is nothing else to change or do. You don't have to mail a paper check even if you selected a paper check within TurboTax. How you decide to pay your CA income tax is between you and CA.