Documentation
Force HTTPS Redirection
Sometimes your website may not load through https:// even when SSL is installed and activated on your domain, this happens on some servers. To forcefully redirect your website HTTP to HTTPS;
Open the ".htaccess" file on the root directory and add the following code at the end:
RewriteEngine On
RewriteCond %{HTTP_HOST} ^example\.com [NC]
RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*)$ https://www.example.com/$1 [R=301,L]
Note: you must replace example.com with your site URL.
I hope this helps.