Hey Dan1307, I’m not sure what you mean by 1 object and multiple elements. When you import your Datasmith inside Twinmotion, please verify which collapse option you’ve selected [ keep hierarchy/collapse material/collapse all]. This option will have an impact on the element structure.
Depending on this, the way to apply materials may differ. see this article for more info;
Once you’ve determined which collapse method you need, you can use the eyedropper to select the material you want to edit.
Here are articles that could be useful ;
Hope this helps
cheers
MC