CalculateRollupFieldRequest

EntityReference Note = Case.GetAttributeValue<EntityReference>("caseid");
CalculateRollupFieldRequest calculateRollup = new CalculateRollupFieldRequest();
calculateRollup.FieldName = _FieldSchemaName;
    calculateRollup.Target = new EntityReference(_EntitySchemaName, Note.Id);
CalculateRollupFieldResponse resp = (CalculateRollupFieldResponse)_service.Execute(calculateRollup);