How to help my nearly 4 yr old with confidence

I like such a failure at times I’ve noticed my little boy gets really shy and goes super quiet around people including both adults and children. He’s a pre school and I understand every child is different. I think he gets shy and overwhelmed in noisy environments. I’ve seen this and his key worker has said they are going to supprt him with his confidence and feelings. At home you would never think the was shy or quiet. Anyone got any tips how I can help him outside of home. He’s starting school on sept and just worry it’s a big wide world and want him to be able to express himself if someone was bothering him .