You don't. If you require to train as a sniffer dog handler, you require to work in a related industry and apply (or have your employer apply for you) to a national training programme. Most programmes will pair dogs (already puppy trained for the purpose and price of dog included in the fees) and new prospective owners/handlers in accordance with their strict criteria - in other words, you might like the look of the Golden Labrador, but the instructors think you'd be better suited to the Spaniel. I can't imagine any of them taking on an unknown quantity i.e. Your dog, from the point of view that all of the dogs on their training schedule have already been pre-trained and assessed as competent for purpose. Training your dog specifically as a drug dog would require the dog to be exposed to the actual scent of drugs e.g. Cannabis, heroin, cocaine etc. Only nationally recognised training centres are licenced to keep small quantities of these drugs. If you attempted to get a hold of any of these kinds of drugs, even just to train your dog, you will be breaking the law and may face imprisonment if caught.