If your device does not show an update automatically, users often turn to manual firmware files. These are typically provided in .zip format and flashed via Recovery Mode.
If the OTA option fails, you must download the local zip installation file directly to your phone's storage. Look for firmware build variations based on the target. oppo f3 nougat update file download top
Top Oppo F3 Nougat Update File Download & Installation Guide (Android 7.1) If your device does not show an update