You can try putting bitter apple spray on the leash and see ow that works. If he is a puppy then he will grow out of it eventually. I would also advise you not to try and pull the leash out of his mouth since he will think you are trying to play.
For the sake of your dogs teeth I would stop using a chain and use a nylon or leather leash so he does not break any teeth since that would hurt and cost way more to fix then some new leashes. When he chews it distract him with his chew toy and praise him for chewing it. Eventually he will learn that it is ok to chew his toys but not his leash.