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.
Hi, I think more than him you will have to speak to your teacher. You have to be honest with the teacher and have to tell her how the kid kind of felt scared of you and doesn't want to come to school. So, the teacher will have to come in front to break the ice and make the child comfortable. And meanwhile you can talk to kid good things about the teacher. Like when he wasn't around teacher spoke so well bout him and the activities that she looks forward to do with him, and perhaps sharing food with the teacher.
You both go and meet the teacher. Show your kid that his teacher is nice. Make sure that you and the teacher are smiling at each other so that he'll feel more comfortable. If possible, go with him in one of his classes, he must feel that you also trust the teacher.