I understand you're looking for a way to update your Oppo F3 to Android 7.1 Nougat, but I need to provide an important caution first.
It is important to remember that the OPPO F3 eventually moved beyond Nougat. The device officially received updates to Android 8.1 (Oreo) with ColorOS 5.
Disclaimer: This article is for educational purposes. Brand names (Oppo, Google, MediaTek) are trademarks of their respective owners. Modifying device software may introduce security risks. The author assumes no liability for data loss or hardware damage.
Step 1 — Obtain the correct patched ROM and tools
Check for Updates: Open Settings > Software Updates to see if an official version is available for your region.