The established best practice is to use a CSV file in which the mapping between the old and new SourcedIds is provided i.e.  one column of old SourcedIds and one column of the equivalent SourcedIds.  This CSV file can either be created manually or, in the case of a large number of SourcedIds, a simple data migration tool must be used. 

IMS is developing a simple SourcedId migration tool to support the creation of the CSV file containing the old/new SourcedId map for Users.  This tool will enable the manual definition of the mapping and also an automated mapping using simple pattern matching on ‘givenName’, ‘familyName’, ‘middleName’, ‘email’, ‘userIds’, ‘username’ and ‘identifier’.  This tool should be available from April 2021.