This field is usually configured by the sFiles Object Setup Wizard. This must be a text field if you plan for sFiles to create and link a SharePoint folder automatically. It can also be set as a formula text field if you want a pre-created SharePoint folder to be displayed on the Salesforce Record.

NOTE: The 'Task' or 'Event' objects behave differently than other Salesforce objects. To set the SharePoint Folder Id field for these objects, you will need to set your folder name field on the 'Activity' object and input the API name of this field into the SharePoint Folder Id Field Override.

To view or change your SharePoint Folder Id Field, go to Salesforce Setup > Custom Code > Custom Metadata Types > click 'Manage Records' next to SharePoint Object Settings and select your object.