Puppy bite grip building is started at the age of 3-4 months. A puppy is trained to chase and catch a bite tug. Puppy bite work training with a builder is the next level of exercising.
The builder is hold horizontally at puppy jaws and moved from side to side. The puppy should bite the tool with full mouth.
Never pull the item hard out of puppy teeth. This may hurt them and interfere further training because of discomfort.
Don't make your puppy to get tired. Let the exercises be shorter, but repeat them 3-4 times.
Play "tug of war" with the puppy. Allow it to win every time the puppy gets a "prize". Give a command to leave the sleeve after the dog enjoyed running with it in teeth.