The Classes + Events page in Debebe Theme is built using WooCommerce products. 

Each tab contains a particular template with products.  

To begin, navigate to the Toolbar > Edit with Elementor > Classes - Item 1

Or go to Templates > Saved Templates > Classes - Item 1 > Edit with Elementor. Control the layout, conditions, rules and styles of the template. 

Read more about the Elementor Templates

The date picker is part of the Extra Product Options plugin:

Read more about setting up the WooCommerce Shop & Archive pages