add_filter( 'asp_results', 'asp_custom_link_results', 10, 1 );
​
function asp_custom_link_results( $results ) {
​
  // Parse through each result item
  foreach ($results as $k=>$v) {
    /**
     * In this context the
     *      $results[$k]->link
     * variable holds the result link. Make modifications to that variable.
     */
    $results[$k]->link  = 'https://google.com';
  }
​
  return $results;
}

// Live results URLs
add_filter( 'asp_results', 'asp_custom_link_meta_results', 10, 1 );
function asp_custom_link_meta_results( $results ) {
    // Change this variable to whatever meta key you are using
    $key = 'custom_url';
​
    // Parse through each result item
    foreach ($results as $k=>&$r) {
        if ( function_exists('get_field') )
            $new_url = get_field( $key, $r->id, true ); // ACF support
        else
            $new_url = get_post_meta( $r->id, $key, true );
​
        // Change only, if the meta is specified
        if ( !empty($new_url) ) {
            $r->link = $new_url;
        }
    }
​
    return $results;
}
​
// Results page URLs
add_filter('asp_regular_search_result', 'asp_custom_link_meta_results_res_page', 10, 2);
function asp_custom_link_meta_results_res_page( $post, $r ) {
    $key = 'custom_url';
​
    if ( function_exists('get_field') )
        $new_url = get_field( $key, $post->ID, true ); // ACF support
    else
        $new_url = get_post_meta( $post->ID, $key, true );
    if ( !empty($new_url) ) {
        $post->asp_guid = $new_url;
    }
    return $post;
}