Here’s a quick htaccess edit that will redirect your domain to a subfolder;
RewriteEngine On
Options +FollowSymlinks
RewriteBase /
RewriteCond %{HTTP_HOST} www.domainname [OR]
RewriteCond %{HTTP_HOST} domainname
RewriteCond %{REQUEST_URI} !subfolder/
RewriteRule ^(.*)$ subfolder/$1 [L]