You can access Hierarchy Manager by logging in to the Hub Console, selecting a profile, and acquiring a lock. Your software license must have Hierarchy Manager enabled in order to see the Data Steward workbench.
Most data stewards have permissions to see Hierarchy Manager in the Data Steward workbench. However, you usually require special privileges to access the Hierarchies tool in the Model workbench. If you cannot see a workbench, contact your Informatica MDM Hub administrator.