In Ktor JWT authentication, How we can securely regenerate token by refresh token or by any other method?

In Ktor Authentication

1. what is realm and issuer
2. How can we regenerate token? If we use refresh token to automatically regenerate. Then in our app, we have to store it in a local database. Then what is the difference between a non-expiring token and this? So what is the right way to do all these things?