How to get the multiple fields values update in one field on view page

Question

i am creating one preprocess_views_view_field for specifc one field.I have 2 fields file name and news link. while need to change or get the those values are pass to field_link_text. I cant achive it

function bootstrap_preprocess_views_view_field(&$variables) {
global $base_url;
$view = $variables['view'];
$field = $variables['field'];
$row = $variables['row'];
$string_values = '';
$string_values_here ='';
if ($view->id() == 'news_block' && $view->current_display == 'page_1') {
    if (($field->field == 'field_link_text')) {
        foreach ($view->field as $id => $field) {
    if ($id === 'field_file_name') {
         echo $string_values_here = \Drupal\Core\Render\Markup::create($variables['output']);
    }
    }
    } 
}
}