The JWTs from the OIDC auth flows can not be refreshed, as mentioned in the docs Using OIDC to get OAuth Access Tokens | Twitch Developers
The iframe error you’re getting is because you shouldn’t be using the login page as in iframe within your site. If you need a new JWT you need to send the user through the auth process again (which if they’re still connected to your app, will be seamless as Twitch will send them right back to your redirect along with new tokens).