Your dog should not growl or bite when being handled. If you are having this more serious problem, please contact your trainer right away.
Begin this where your dog is already relaxed.
Hand the treat directly to your dog. That way your dog can stay in position while you continue the exercise. It is probably easiest on your dog to be in a down when you start.
First, consider all the ways your dog may experience touch and need to tolerate it. Think of vets and groomers. Things your dog will need to do during their lifetime will probably include:
With this in mind, create mock scenarios and help your dog get used to any way that they might be handled. Create positive scenarios and practice them.
Your dog should allow you to take hold of his paw without any signs of stress.
If you are seeing signs of stress, go back to the beginning and work up again, but do it more slowly.