Update a field without changing the node
Let's try this code: 

function MODULE_NAME_node_presave(Drupal\node\NodeInterface $node) {
  $node-&gt;set('FIELE_NAME', 'FIELD_VALUE');
}


OR

use Drupal\node\NodeInterface;

function hook_entity_presave(Drupal\Core\Entity\EntityInterface $entity)   {
  if ($entity instanceof NodeInterface) {
    $entity-&gt;title-&gt;value = 'testing';
  }
}