I don't know how it works for rats, but I assume it is like with dogs. If you have already a trained dog, you make the same exercises with the trained and the untrained dog, so the untrained dog can just watch what the trained dog does and imitate it.

That's not how you would typically train a working dog.

I imagine it depends on the work?

I am not an expert here, but am a bit familiar with how rescue dogs are trained and this is a method in use.