1. Invoke the interfacesendVerifyCodeWithUserName, where the mail is the email to replace the bound account email. For example, if the current A email is the account email, and you want to switch the B email as the account email, then the username is the B email, type is 7, and send the bound email verification code
2. Call the interface changeUserName, sid is the sid of the A email, which can be obtained through User.sid, and by setting the username as B email, the operation can be successful