Every new site that you create will be HTTPS enabled. If you want to reload the demo site, you can do the following:
sudo /opt/bitnami/bnhelper-tool and set up let's encrypt with default settings. You did this step already.
1) Go to http://YOUR_SEVER_IP/neos/administration/sites
2) Click on
Add new site
3) Click on
Import a site
4) Access to your main site again
Let us know if this works for you.