After the App Catalog is created under the Apps tab, navigate to the Policies tab. You can either create a new policy or choose to edit an already existing one. From Android/iOS > App Management, select App Catalog and click on ‘Configure’. Click on ‘+Add Catalog’ and choose the desired catalog. Click Done. Associate targets and save the policy. The catalog will be deployed to the device.
Kindly use the help link for App Catalog for more info.