Click here to reference the steps for updating district codes for all contact records.
Although District Codes typically do not change unless there is a new census, we do update and maintain them quarterly.
The reason you, as the client, have the option to update District Codes manually is because when a record comes in through an advocacy registration it will get a district code assigned to it as long as it has complete and real address.
If the record comes in through most any other source a District Code will not be assigned to it.  For example, thon registrations, donation forms, etc.
For this reason you would use the District Code tool to update these records in Sphere, not because the district codes have changed, but because not all records in your DB will have them based on how they came into the database.
NOTE: A record must have a complete and real address in order for advocacy to district records correctly.
Once you have submitted the District Code update, if it has not completed within 24 hours please Chat with Support and reference this article.