If you are trying to change the texture of some of your layers, but some of them are not replaced by the automatic function, you can replace them manually.
Open your Project tab and you should see the file for your model.
Now select the layer where you want the texture to be replaced from the parts list. Open your file in the Project tab by clicking the gray arrow, and within your file open the Model Image folder as well. Now you should see every layer from your model, including the new textures. Right click the new texture from this list for the layer you selected, and click "Set as input image for selected ArtMesh".
The texture should display correctly now.