Press and hold simultaneously until the "Software Upgrade" screen appears.
Power off, then hold to enter the recovery menu. Press and hold simultaneously until the "Software Upgrade"
Extract the downloaded firmware and move the file (and any required data zips) into the dload folder. Power off your phone. Press and hold simultaneously until the "Software Upgrade"
Select > eRecovery mode > Download update and recover . Press and hold simultaneously until the "Software Upgrade"
You can find the official flash files and drivers at the following reputable sites: Provides direct downloads for C431 stock ROMs (Android 9 and 10).