Do sealant works on cylinder head gasket?

Depending on what type of leak you are trying to fix sealants that get put in the radiator may work for a while. But my experience says not long.

If you are installing a new one, do not use any sealant not recommended in the gasket kit.

If you are blowing white smoke out the exhaust, there are a couple of different brands that have copper in them. One is in a bottle, mostly clear liquid with the copper settled to the bottom. If the coolant is only going out the exhaust, follow the instructions and I have never had this fail. If coolant is getting in the oil or exhaust is getting into the radiator it will not help.