You can set the texture of your models by using the Set Main Texture node.
Dereference this node from the object whose texture you would like to change.
Drag your texture image file from the assets tab (textures can be found in the texture filter) into the New Texture parameter and add the node to the line of execution.
If you would like the texture to be applied to the model on startup make sure to place it right after the setup node.
Click to download the sample asset used in demonstration.