Heater works on the lowest setting but blows cold air on the other settings

Good morning,

You can try it but results may vary. The stuff is very acidic and could damage the core and cause it to leak. That puts you out of the pot and in the fire.

https://www.2carpros.com/articles/car-heater-not-working

I would remove the hoses from the heater core and use a garden hose to flush the core. Go back and forth in the core until you get a good even flow in both directions. Beyond that, the core would have to be replaced.

https://www.2carpros.com/articles/replace-heater-core

Roy