Redirect to HTTPS
In order to redirect to HTTPS, add an .htaccess file to your website root with a redirect directive.
The .htaccess file should be located in the root of your website, where your main index.html/php file is located also.
Be aware that a .htaccess file is a hidden system file, which might not be displayed by default by your FTP application.
Add following redirect to this .htaccess file to redirect all HTTP calls to HTTPS:
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
To have that working, the mod_rewrite module has to be available, which should be the case in most hosting server environments.
For more information, check following page: https://wp-mix.com/htaccess-redirect-http-to-https/