add_filter('site-reviews/field/select', function ($field) {
    // 1. enter your custom select field name here...
    if ('your_custom_field_name' === $field['path']) {
        return $field;
    }
    // 2. set your custom select option values here...
    $field['options'] = [
        'val_1' => 'Value 1',
        'val_2' => 'Value 2',
        'val_3' => 'Value 3',
    ];
    return $field;
});