You would need to file proceedings for visitation and/or custody based upon the changed circumstances. You should consult a CA attorney as soon as possible to discuss your specific facts and issues.
I hope you found this answer helpful and if so, please let me know by clicking the "Mark as Helpful" button at the bottom of this answer. It’s easy and appreciated. You can also choose a "best answer" if you wish.
This advice is not meant to create an attorney-client relationship and is a general anwer to the question posed.
Sign up to receive a 3-part series of useful information and advice about child custody law.