When training fetch, place the object in front of him to allow him to play carefully before you throw it away and tell him to find your lost items. Of course, nothing can be too far away in the beginning stages of training. You can guide the dog to retrieve the misplaced items by following 1 meter, 2 meters, or 3 meters. After the dog successfully retrieves the item, it should be praised and given a treat. Petting and treats from the owner are excellent ways to show appreciation.
Simply ignore him if he returns alone and keep throwing toys until he brings them back to you. If he is not understanding this, you only run over with food for the toys in his mouth, pull away quickly during training, and then gradually increase the distance.
Keep each session to 10-15 minutes, 2-3 times per day, and avoid making them too long. The best time to train him is about 30 minutes to an hour before he eats.
And once he's in it, you can't just stop training; you have to wait until the dog has mastered the material and formed conditioned reflexes.