The template package uses PHP Mobile Detect to serve up the optimized layout based on device. If you are on a Desktop and want to view the Tablet layout use this link. If you want to view the Mobile layout use this link. To switch back to a Desktop use this link.
This content is located in the file at: /languages/english/html_includes/YOUR_TEMPLATE/define_main_page.php
You can quickly edit this content via Admin->Tools->Define Pages Editor, and select define_main_page from the pulldown.
NOTE: Always backup the files in /languages/english/html_includes/your_template