1997 Chevy Silverado 02 Sensor

Engine Performance problem
1997 Chevy Silverado V8 Four Wheel Drive Automatic 165K miles

My OBDII reader indicates I have an O2 sensor issue, there are four sensors on my truck (pre and Post converter). Can you tell me how to indetify which senor has the issue from the OBDII identifier? ( drivers side front / rear, Passenger side front / rear)

Thanks!