How to write if statement if box is checked

I created this function to create a new element in WPBakery. I have this part where user can check an item. But I can't figure out how to write the if statement. I.e if( ITEM IS CHECKED ) { $markup = "Html here"; } return $markup;

Here's my code for the checkbox:

array(
      'type' => 'checkbox',
      'heading' => esc_html__( 'Download App', 'mysite' ),
      'param_name' => 'download_app_badge',
      'value' => array(
        esc_html__( 'Yes', 'mysite' ) => 'app_checked',
      ),
      'std' => 'app_checked',
    ),

Here's an image of the front-end widget: here