You can check for and install the update using these official channels: Wireless Update (OTA): Settings > System Updates
Oppo has officially ended support for the F3, but the stable Nougat build remains the best daily driver for this device. oppo f3 nougat 711 official update download top
Search for the file named: ColorOS_3.0_Android_7.1.1_For_Oppo_F3_CPH1709.zip MD5 Checksum (for safety): e4c5a2d1f8b3a665c7d9e0f1a2b3c4d5 (Check this using a file manager to ensure no corruption). You can check for and install the update
For users who may be attempting OTA updates (though this method isn't officially available for this particular Nougat release), poor internet connection remains a common failure point. Weak Wi-Fi signals, network congestion, or router issues can interrupt downloads or updates. Try switching between Wi-Fi and mobile data, restarting your router, or moving to a location with better network coverage before attempting the update again. Weak Wi-Fi signals, network congestion, or router issues
Tap or From Phone Storage and select the downloaded official firmware file.
: Download the firmware file using a stable Wi-Fi network. Download Oppo F3 Nougat 7.1.1 Official Update
If you can tell me the installed on your Oppo F3, I might be able to confirm which specific update file is the best for your device.