Additional data does not appear in classification

Hello friends,

I have tried to find materials with the "material by class" search help and when I selected

more then one material it told me I need to set the "multiple selection" indicator in the class.

I have been told the indicator appears in the additional data in the classification but I can't find

it. If you know what can I do please help me.

Thanks in advance,

Eitan Illuz.