Contact a school and see what requirements they want you to have. A school in China I applied to didn’t want me to have anything because they wanted to teach me how they wanted their students to be taught. Their only requirement was that I be a native English speaker. But it’s entirely up to you. You can take a TESOL or CELTA however it’s quite expensive and not necessary. Having said that. It would give you some tools on how to teach, complete lesson plans and speak in front of others.