htaccessにリダイレクトの設定を書く

<IfModule mod_rewrite.c>
      RewriteEngine On
      RewriteCond %{REQUEST_URI} ^form.php
      RewriteCond %{SERVER_PORT} !^443$
      RewriteRule ^(.*)?$ https://%{HTTP_HOST}$1 [L,R]
</IfModule>