How do you repair a spinnel on a left front wheel of a S10 Chevy pickup?

Depends on what broke but 99.9% of the time, you replace the whole spindle. cheapest is from the junk yard.

If the damaged spindle is from bearing failure or a bent shaft.It would be best to replace the steering knuckle.This would require the removal of the spring.Use of a spring compressor is a Must or you will not be able to reconnect the ball joints.

just replace it, cheap enough. no need for a srping compressor. just keep a jack under the lower control arm with the truck on stands.

I agree with Andrew, the weight of the truck will be enough to act like a spring compressor and save that money.

I must strongly disagree with DeBo13 and Andrew .If the shock is removed from the lower control arm,and you separate the steering knuckle.A spring compressor is needed .If the shock is not removed this will hold the arm up and spring compressed.