How do you fix an 02 sensor in a 2000 Chevy blazer?
Do you know which sensor is bad? Have you had the computer scanned? most of them just unplug from the wiring harness and you unscrew the sensor out of the exhaust pipe either before or after the catalytic converter. If they are bad you can generally shake them and you will hear them rattle due to the porcelin breaking.
If it is electronic (not cable driven) and both the speedometer and odometer are not working I would suspect the VSS (Vehicle Speed Sensor) is faulty. The VSS can be found on the tail end of the transmission. If only the speedometer doesn't work I would suspect the dash cluster has to be replaced with a new or good used one. Really need to know what year S10 Blazer you have.