The good news is that you only need to amend one of the returns; the IRS (and state) will disregard the other separately-filed return when they receive your amendment. We suggest amending the one that's more complicated (that way you don't have to re-enter all that info), but it's up to you to decide which one to amend.
You'll need the TurboTax Desktop software to do the amendment. See this TurboTax help article for more information and steps.
Then, use the Federal return that you amended to follow through to the state return.
See California Schedule X instructions for more information.
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