WP Job Manager – connect filter to an existing widget-field

I’m using WP Job Manager in combination with ListingEasy (theme).

I have made an extra search filter, based on a new custom form field. However, now I want to refer to an existing field, named: working_time_text__day. It is already displayed in a widget on the listing-page, however I’m not sure how to connect to those fields.

Hereby the code with which I created the filter:

/**  * This code gets your posted field and modifies the job search query  */ add_filter( 'job_manager_get_listings', 'filter_by_salary_field_query_args', 10, 2 );  function filter_by_salary_field_query_args( $  query_args, $  args ) {     if ( isset( $  _POST['form_data'] ) ) {         parse_str( $  _POST['form_data'], $  form_data );          // If this is set, we are filtering by salary         if ( ! empty( $  form_data['filter_by_salary'] ) ) {             $  selected_range = sanitize_text_field( $  form_data['filter_by_salary'] );             switch ( $  selected_range ) {                 case 'vrijdag' :                     $  query_args['meta_query'][] = array(                         'key'     => '_job_salary',                         'value'   => 'vrijdag',                         'compare' => '==',                     );                 break;                 case 'zaterdag' :                     $  query_args['meta_query'][] = array(                         'key'     => '_job_salary',                         'value'   => 'zaterdag',                         'compare' => '==',                     );                 break;                 case 'zondag' :                     $  query_args['meta_query'][] = array(                         'key'     => '_job_salary',                         'value'   => 'zondag',                         'compare' => '==',                     );                 break;                 case 'maandag' :                     $  query_args['meta_query'][] = array(                         'key'     => '_job_salary',                         'value'   => 'maandag',                         'compare' => '==',                     );                 break;             }              // This will show the 'reset' link             add_filter( 'job_manager_get_listings_custom_filter', '__return_true' );         }     }     return $  query_args; } 

In the picture below the script of the side-widget. I want my filter to search on the working_time_text__day, instead of the salary custom field.

enter image description here

To which value I should change the ‘key’ in the query_args?