The Kennel Club do not run courses for dog trainers. The usual route is to join a dog training club, become proficient at training your own dog(s), attend seminars and dog training courses run by dog clubs and then start taking classes within your own club. After many years of hard work you will be able to maybe start you own club or offer one to one training.
If you mean the sort of training that is shown on 'reality' TV shows, dog 'behaviourists' are just dog trainers with the
nouse to make more money out of it by charging a fortune to tell people to shake a coke tin full of pebbles at their dogs. Barbara Woodhouse was only doing what most of us have been doing for years, but because she was eccentric, the TV people managed to make a 'star' out of her.
You can even take dog behaviour courses on line! How on earth anyone can call themselves a dog trainer without having even touched a dog amazes (and frightens) me.