How do I assign materials to internal surfaces?

Development World Creation
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Geometry Collections User Guide | Unreal Engine 5.4 Documentation | Epic Developer Community (epicgames.com)
“Change the Materials of Geometry Collections”

I created my geometry collection like the one shown after “Deselect the Show Bone Colors checkbox” using 2 SM_ChaosPrim_Box and 1 SM_ChaosPrim_Bully actors whose assets were migrated from Content Examples.

  • The Materials section is not like what is said in “each original Material ID has been duplicated from the source Asset”, there are 2 materials that are not duplicated. Then how can I assign the internal materials.

Thanks.