sync a new custom attribute (User emp number) from flat file database (*.CSV) to FIM to Active directory

FIM is already deployed and functional in the environment for the user object and its attribute to flow from data source (*.CSV file) to FIM and export in to Target i.e. Active directory.
New custom attribute will be published in the CSV file for each user object. What steps needs to be performed on the Forefront Identity manager so that the new attribute is imported from CSV file and gets exported to Target (AD)

please provide the technical steps