<?php

use \Drupal\node\Entity\Node;

// Load all nodes and delete their title and description field values.
// This will force using the default values for these metatags fields.
foreach (Node::loadMultiple() as $node) {
    foreach ($node->getTranslationLanguages() as $langcode => $language) {
        $translation = $node->getTranslation($langcode);
        $metatags = unserialize($translation->field_meta_tags->value);
        unset($metatags['title']);
        unset($metatags['description']);
        $translation->field_meta_tags = serialize($metatags);
    }
    $node->save();
}