MODIFY TEXTURES ON 3D OBJECTS
If you have imported a 3D object that has a texture applied to it, that texture will show up as a sub-layer with your 3D layer. To modify or replace the existing texture, simply double-click directly on the texture name in the Layers panel. A dialog will open with the 2D texture. Make whatever changes you need, then close and save the document. Just like a Smart Object, it will update automatically in the main document.