SSH login is usually handled by the the server provider. Cloudron does not have a UI to manage SSH login methods. If you are locked out of your server, usually your VPS provider has a way to reboot the server with a SSH key setup or a reset root password.
Otherwise if for some reason this does not help in your situation you can try to enable Cloudron remote support in the support view of your Cloudron dashboard and then send a mail to firstname.lastname@example.org with your domain details. This may allow us to reset your SSH login details.
Admin credentials for mongo are really internal/implementation details. In general, do not make configuration changes to the mongodb instance because it may not work across all apps. This is the reason why all the databases are "locked" down and not exposed to users for easy access.
That warning said, you can do docker inspect mongodb | grep CLOUDRON_MONGODB_ROOT_PASSWORD to get the root password.