Exercise is not the answer on its own
The instinctive response to a busy dog is more exercise. With working breeds this often backfires: a dog conditioned to run for two hours a day becomes a dog that needs two hours a day, and none of that teaches it how to stop.
What these dogs are missing is not mileage. It is a trained, reinforced way to be still while something is going on.
Pay the stillness you did not ask for
The most effective settle work looks like nothing at all. Sit down with a book and a pot of food. Every time the dog lies down, calmly place a piece of food between its paws. Say nothing. Do not cue anything.
Within a few sessions most dogs are offering the down deliberately. You have not trained a command; you have changed which state the dog thinks pays, which generalises far better than a cued down ever does.
Give it a place
A defined mat or bed makes the behaviour portable. Once the dog is settling reliably on it at home, the mat can go to a friend's house, a café, or the vet's waiting room, and it carries the trained calm with it.
This is general guidance, not veterinary advice. If your dog is showing fear, aggression, or a sudden change in behaviour, speak to your vet before starting a training plan.