If you own a Nokia 3, you should have received the over-the-air update notification for December 1 Android security update. While this update would have been more exciting if it had brought Android 8.0 Oreo, which is already available for Nokia 8.
The build number of this new update is 00WW_2_15H. Nokia's instructions explain that for a successful installation, the battery in your phone should be at least 50% charged and your device should be connected to a Wi-Fi network or LTE.
If you haven't got the notification of this new software update yet, Just go to Settings - About Phone - Software updates, and It will automatically start downloading the latest update. The update will take around 10-15 minutes to get Installed on your device.