by default Your subdomain will point to the subdomain Document Root if you didn't specify the Document Root as shown on the image below

if you didn't change the Document Root of the subdomain you will need to edit the subdomain and add /public to it as shown on the image below

if you installed the app on a sub folder (Example : /public_html/support/ ) you need to add your folder name to your settings.php file 'app_parent_folder' => 'support'

1. After making these modification you need to clear the app cache
   Settings page -> SYSTEM CACHE

Although installing the app on sub domain or a VPS is recommended (To keep all your app files out of the public_html folder)