Click Concrete Design > RC Materials to view the RC Materials table. (This will list any materials that have been defined in the model, not just concrete materials.)

This table contains the materials that have been defined in Tables > Materials, but it lists their concrete design related properties as opposed to their analysis properties. The purpose of this table is to specify values for concrete strength, rebar yield strength and shear rebar yield strength for any concrete materials that are involved in a design.
Tip: The materials have probably already been assigned to the members in order to get an analysis. So at this point, there is no need to Assign anything specific to members. It is only necessary to specify the material strength values for any materials that are actually involved in a design.