open the CA return, Activate the Sch X by opening it and entering the year at the top, now go back and make the changes, your Sch X and new CA 8879 (if youve marked the amended for EFiling on the Fed Info Worksheet) should show the refund difference.

I have no problem preparing the Calif Form X, but I can't get it to efile. No Fed return needed, just a Calif tax  w/h issue.

You got the CA chosen in the drop down list of the Fed Info worksheet  to EF the CA Amended return?