Thêm đoạn code này vào file .htaccess
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*)$ https://www.yoursite.com/$1 [R,L]
</IfModule>
Nguồn: wpbeginner.com/wp-tutorials/how-to-add-ssl-and-https-in-wordpress/