Getting state tax back for having no CA sourced income as nonresident

My previous CPA has been filing CA state tax for me on year 2018, 2017, and 2016. I live in Germany since 2013 and has no CA sourced income. I would like to make amendments from 2016 - 2018 and get the tax paid to the State back. How would I do that? Should I file a 1040X and 540 NR again and adjust all the dividend/interest/ income to 0 on the 540 NR? I've purchased 2018 Turbotax and would like to start with it.

 

I made an amendment on year 2016 on a different topic in Feb 2019. Now I would have to file a second amendment on year 2016 because of the state tax. I have not heard anything back from the 1st amendment. The due date for me based on the 3-year rule is 15 Apr 2020. How should I do it properly?

 

thank you!