After migrating from 11g to 12c, you must manually migrate the WebLogic users in to your 12c domain. You can do this by exporting the security data from a security realm and importing it in to another security realm. Security data includes authentication, authorization, credential map, and role data.
Understand when you would want to migrate security data. See Overview of Security Data Migration.
Understand the concepts associated with importing and exporting security data. See Migration Concepts.
Understand which formats and constraints are supported by the WebLogic Security providers. See Formats and Constraints Supported by WebLogic Security Providers.
Note:
You can only export and import security data between security realms in the same WebLogic Server release.