This Id is typically set by the setup wizard, though it can be overridden.  Changing this value is best accomplished by running the sFiles Configuration wizard again. If this is not possible, be sure to update the Document Library Path at the same time. This Document Library Id can be overridden with a field value at the SharePoint Object Settings level as well as at the sFiles Enterprise component instance level.

 

To view your Document Library Id, go to Salesforce Setup > Custom Code > Custom Metadata Types > click 'Manage Records' next to SharePoint Settings > Default.