As a first step, add references to the latest version 9 assemblies
https://www.nuget.org/packages/Microsoft.CrmSdk.CoreAssemblies/
In the below sample code, we are creating an Auto number attribute in Contact Entity.
This is how the fields shows up inside contact form.
Using UpdateAttribute Request we can update the format for the AutoNumber field.
And also, we can have multiple auto number fields for an entity as shown below.
Sample Code
CreateAttributeRequest createAttributeRequest...
