8 – How to update changed date for a node

I am migrating content from Drupal 7 to Drupal 8. Migration works fine except the changed date for node get changed to the current time. I want to set the timestamp to the Drupal 7 timestamp. I have tried out the following but it is not working.

        $changed_date = $node->getChangedTime();
        $node->set($source('parent_field_name'), $paragraph_target);
        $node->changed->value = $changed_date;
        // print_r($changed_date);die;
        $node->save();