Heroku - NodeBB Documentation
make sure you have port 80 and/or 443 open on your firewall. I see 80 is open (I get the "Welcome to Nginx" message). So now you need to make a few changes in your nginx config for it to redirect 4567 to your site on 80/443 (http/https), as currently it is set to the nginx page.
The docs has a config you can use, just make the changes like Pitaj has suggested and for https, you will need a certificate. Lets-Encrypt is free
**Edit to add: Don't forget to restart nginx to use the new config
