I want to rescind an Unlawful Detainer that I filed and had served. How do I do it?

Until the tenant has relinquished possession of the rental unit to you, you can leave the unlawful detainer action open.  You can enter into a written stipulation with the tenant to move out on a certain date, and then the unlawful detainer will be dismissed. Here is the stipulation form: http://www.courts.ca.gov/documents/ud115.pdf