You can use placeboards to steady your dog up. Start by having your dog sat on a placeboard and then walk out and place the dummy or ball down. Note if your dog is super excited around tennis balls you can use this exercise to steady them. Throwing the dummy/ball is exciting and therefore by removing the excitement of the throw you can steady your dog up. Calmly send the dog and then guide the dog back onto the placeboard staying calm while taking the retrieve. Do not fizz the dog up by praise either. Praise can be given in a calm way too. Do the sessions over and over until you get the dog steady. Remember to keep each session short, but you can repeat later in the day or the next day.