Using htaccess to change document root [closed]

add the following lines to the .htaccess file in the public_html folder:

RewriteEngine on
RewriteCond %{HTTP_HOST} ^domain-name.com$ [NC,OR]
RewriteCond %{HTTP_HOST} ^www.domain-name.com$
RewriteCond %{REQUEST_URI} !folder/
RewriteRule (.*) /folder/$1 [L]