Below are download links for OPPO android smart phones.
Download, Extract and flash with the required tool
Note
Make a backup of your system apps & userdata before you flash or upgrade your device with any of the firmwares below because after the process you will lose all data on device
FLASHING INSTRUCTIONS
To flash OPPO MediaTek divices, use SP Flash Tool or any other tool which can flash MTK devices (WiseLink tool, SP MultiPortDownload Tool, etc)
To flash OPPO Qualcomm devices, below use GNQC, eMMc DL Tool or any other tool which can flash QUALCOMM devices