You can force an HTTPS connection on your website by adding these rules in your website's .htaccess file:
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https: //%{HTTP_HOST}%{REQUEST_URI} [L, R=301]
The .htaccess file needs to be located inside the site's document root folder. If your website is in a sub folder, then the .htaccess should be placed in the corresponding sub folder.