Cal. CCP § 398

(a) If a court orders the transfer of an action or proceeding for a cause specified in subdivisions (b), (c), and (d) of Section 397, the action or proceeding shall be transferred to a court having jurisdiction of the subject matter of the action upon agreement of the parties by stipulation in writing, or in open court and entered in the minutes or docket. If the parties do not so agree, the action or proceeding shall be transferred to the nearest or most accessible court where the like objection or cause for making the order does not exist.

(b) If an action or proceeding is commenced in a court other than one designated as a proper court for the trial thereof by the provisions of this title, and the same is ordered transferred for that reason, the action or proceeding shall be transferred to a proper court upon agreement of the parties by stipulation in writing, or in open court and entered in the minutes or docket. If the parties do not so agree, the action or proceeding shall be transferred to a proper court in the county in which the action or proceeding was commenced which the defendant may designate or, if there is no proper court in that county, to a proper court, in a proper county, designated by the defendant. If the defendant does not designate the court as herein provided, or if the court orders the transfer of an action on its own motion as provided in this title, the action or proceeding shall be transferred to the proper court as determined by the court in which the action or proceeding is pending.

(c) The designation of the court by the defendant as provided for in subdivision (b), may be made in the notice of motion for change of venue or in open court and entered in the minutes or docket at the time the order for transfer is made.