When you are given access to the user to access the MFD application, you need to give field level permission to the custom object named "Excluded objects" and its fields as well as "View all" object access permission. This permission you can assign by using custom permission set or directly assigning permission to the user profile.
Also, the app provides following two permission sets which admin user can assign to users based on their requirements -
- Mass File Download Permissions (Admin)
- Mass File Download Permissions (Non-admin)