Already installed SSL certificated for your website ( let’s encrypt or purchased SSL ). See how to force https:// via .htaccess file configuration.
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
One more step to complete your rule. Go to Question2Answer dashboard, modify the option Preferred site URL: https://yoursite.com . That’s right.