Low beams on my chevy blazer stopped working all at

Replacement bulbs aren't very much money - replace one and see if it works. If they haven't been replaced since it was manufactured, it's probably time.

You need to first establish that you have current to the headlight in question. With it being so flaky in how it is working I would bet that your connector is bad at the light. Grab a meter and see if you are getting your 12 volts to the connection. Cleaning it out may help you for a while.

Blown fuse.

Replace The Bulbs

I believe in a Chevrolet you push the left stalk (turn signal stalk) foward for high beam and back for low. If you have the lights on low beam and pull the stalk back, you'll "flash" your high beams.

Try changing the headlights....some headlight high beams will work even when the low beams dont

maybe a fuse the fuse box is under the drivers side passenger seat . sometimes ive seem them get something spilled on them and i had to wiggle the fuses to clear the corrosion

I would say your light switch is either dirty or bad.
www.rockauto.com

check the low / hi beam switch

check the head lamp dimmer swicht