After plugin activation new section Filter is automatically displayed on existing specification attributes settings.
To change specification attribute's settings in NOP admin go to /Admin/SpecificationAttribute/List.
If you are creating a new specification attribute, then first you need to save the attribute, before this action filter section is not displayed.
In this new section Filter a button is displayed, which defines if specification attribute is used as a filter or not.
By default attribute is defined as not a filter - text Is not filter is displayed on button.
When button is activated (specification attribute is marked as filter), then text Is filter is displayed on button.
When NOP user changes button status, then this initiates background process in NOP, which finds all products in NOP, which have the same specification attribute, and changes attributes property Allow filtering value according to button status.
NB! Plugin changes this specification attributes Allow filtering value for all products, which have this attribute applied. Manual changes in NOP can not be done as plugin overwrites it. If integrations (e.g ERP, PIM) are used, then integration can not define exceptions as plugin overwrites the value.