My Chevrolet optra2011 cooling fan high speed
If you're talking about the heater blower inside the car, high speed out but others are fine, it's either the resistor for that speed or the dashboard switch.
I mean radiator fan, This fan is only working on slow-speed high speed not working?
It's most likely a relay. Might be the cooling fan temperature switch; there might be two. Relays are easy to check. find the relay and replace it; you can even replace it temporarily with another one with the same rating in the fuse box just to see if this works. Getting to the switch/s is more difficult and you should have a good manual specific to your car for this.