Change of Address are processed through the Office of the Assessor. Click here: https://www.ocassessor.gov/faqs/changing-mailing-address
You can update your mailing address by submitting the Change of Mailing Address Form to the Assessor's office:
Orange County Assessor
500 S. Main Street, First Floor, Suite 103
Orange, CA 92868-4512
or
P.O. Box 628
Santa Ana, CA 92702-0628
Fax: (714) 834-2565
Phone: (714) 834-2939