If a preschool has a bad impression about his teacher since first meeting pa lang, how do you convince him to go back to class and listen to that teacher?

Hello, You can make the child meet the teacher again in an informal way and try to make out things at ease with the teacher. Take the teacher in the loop so that she too tries to make him feel at ease. And by bad impression do you mean that he found the looks of the teacher being strict? If so, then you can make the child understand that looks do not define how the person is. She may look strict but may be a very loving teacher. This has happened with my daughter as well. Her nursery teacher looked serious kinds and my daughter did not gel with her initially and kept to herself but soon she became the best teacher for her.