The Catalog Manager appears in the OBIEE Client Menu. When you open it, you have to open the catalog by clicking on File -> Open Catalog.
You can choose if you want to open the Catalog online or off-line.
Once you have logged in, you can see Catalog objects in a Folder structure. Locate the folders you want to export and select Archive from the File Menu.
You have to specify the name and the path for the exported file.
Once you have exported the file you need, you have to load it in the new Catalog.
Close the Catalog and open the Catalog you want to migrate your objects to. Locate the location you want to import your objects to and select Unarchive. You will be asked to select the import file and click ok to complete the migration.