Hello!
In Unreal the materials of the objects are defined by “Material Slots”
By default every object has one Material Slot, so that material will be applied to all faces of the Mesh.
The correct and most efficient way to make an object have more than one material is to edit that object in a 3D program and give it more Material Slots.
Although I have read about users using masks of material to do so.
Now, that’s it’s not the best thing to do, and I even think it’s more complicated, but you can try that too.
I leave you the link about the documentation in Material Slots:
I hope it helps you!