Show your dog the treat and then toss it about four feet away from you where your dog can see it. Your dog will pull to get to it but you should be well-anchored so that you are not yanking them back when they go for it! Remain silent and still. The instant your dog creates slack on the leash, say your cue in an excited tone and then run with them to the treats so they can gobble them up. Repeat 5x. You should find that your dog loosens up the leash sooner and sooner with practice.