Heet fuel additive does work to remove water from a gasoline tank and the gasoline but only if there is a little water in the gas tank and there's more gasoline than water in the tank.
If the gasoline has a gallon of water or more in the gasoline and tank then Heet will not work and you'll have to drop the gas tank and drain it out and clean and dry the gas tank out before putting it back on and filling it back up with gasoline.
But if you have natural moisture in the gasoline tank and your engine is sputtering and running rough then adding a bottle of Heet fuel additive to the fuel tank will certainly help in absorbing the water in the tank and then it helps to mix the water with the gas so it gets burned off in the engine.
I've used Heet fuel additive for years and add a bottle of it every second gas tank fill up and it's kept water out of my gas tank.