Searching "oppo a57 software update 7.0 download" brings up dozens of fake sites. Here is what to watch for:
Stick to oppo.com and trusted recovery methods. If you already downloaded a suspicious file, run a malware scan immediately. oppo a57 software update 7.0 download
If OTA fails, download the official firmware package (Oppo calls it "Stock ROM"). Searching "oppo a57 software update 7