<?php
use Microsoft\Graph\GraphServiceClient;
use Microsoft\Graph\Generated\Models\Security\RetentionLabel;
use Microsoft\Graph\Generated\Models\Security\RetentionDurationInDays;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new RetentionLabel();
$requestBody->setOdataType('#microsoft.graph.security.retentionLabel');
$retentionDuration = new RetentionDurationInDays();
$retentionDuration->setOdataType('microsoft.graph.security.retentionDurationInDays');
$retentionDuration->setDays(2555);
$requestBody->setRetentionDuration($retentionDuration);
$result = $graphServiceClient->security()->labels()->retentionLabels()->byRetentionLabelId('retentionLabel-id')->patch($requestBody)->wait();