Important :- It is recommended not to add any form or submit button inside checkout page externally.
1.After activating the plugin go to your checkout page and make sure the page template is “Elementor Checkout”.see screenshots
2.Add some product to cart before editing checkout page.
3.Remove shortcode [woocommerce-checkout] from checkout page and click “Edit with Elementor” to start designing .
4.Import your downloaded layouts or create your own
5.Save all the settings and visit your checkout page.