Unless you are new to driving or are getting into motorsport, I would not recommend taking up left foot braking.

Training your left foot to use the brake on public roads is a very bad idea, in my opinion. You'll find it very difficult to correctly judge how much force is required to use the brake pedal and this means you may brake harder and faster than you intend, creating a potential accident scenario for the driver travelling behind you.

That said, if you have your heart set on using your left peg to apply the brakes, I'd recommend speaking to a driving instructor who will provide some advanced lessons on this technique.

I would question what benefit left foot braking would have in everyday driving situations. When you are not braking, your left foot will be on the footrest, which means it will probably be quicker and easier to simply transfer your right foot to the brake.