@hotsawce
First, if you are a passive investor, I'm not sure this is CA income just because the company is located there. I want to ask for a second opinion. @TomD8
Assuming it is CA income, this is what I expect should happen. Open your Turbotax file (after saving a backup copy of the original in a safe place) and start the amending process. Click to Add a State (California), you will need to pay for the California module since Turbotax includes "one free state" and you would have had to pay anyway if you filed with California originally.
You have no changes to make to the federal return. Do California next. Indicate you are a non-resident. You would allocate 100% of the S-corp income to California, but zero percent of all your other income. Once you finalize California, revisit NY and run through the interview steps. You should see that New York will give you a partial credit for the California tax. (The credit won't be more than the NY tax on the same income would have been. So if the CA tax on the K-1 is $1000, and NY tax on the same income would have been $800, you will get an $800 credit on your NY return.)
The CA return will be an original, Turbotax should let you e-file it (if it is for the current season) or you can print it and mail it in. The NY return should be handled as an amended return, and you should get a refund from NY. NY allows e-filing amended returns. Your federal return should not change, so you don't have to file it and you probably won't even be given the option.
