Please try the following function,
Call transaction CLMM --> Enter class type and class --> Find characteristics of the class using the option "Chars of Class" --> select the relevant characteristics and assign the target object --> to do so, click find object and then select the option "Find in initial class" --> you'll get the list of object, here filter it by object category "Material" --> Select the relevant objects and carry out a mass change.
Note: Mass processing is possible only for the objects that posses same class type.