Get your taxes done using TurboTax

In TurboTax Online, this will be entered during the initial interview questions as you start the California return. If you navigate to Tax Home > State taxes > California & select Revisit 
During the interview screens that ask you about Residency status, etc., you should eventually see a menu that looks like this one (example): 

That is where you will enter your state capital loss carryovers for the year.