There is no specific training needed, but be sure to place the jacket following the instructions.
It's a good idea to introduce ThunderShirt to your dog when they are happy and relaxed. Treats on/around the jacket can be a great way to encourage your dog to investigate it and start to build a positive association with ThunderShirt. Once your dog is comfortable with ThunderShirt itself, place it on your dog and reward them for relaxed body language. Lastly, if they continue to be comfortable, gently use the hook and fasteners to adjust to the correct fit.