If the coolant level is just a bit too high, the excess will be gradually lost through evaporation. If the coolant expansion reservoir tank is too full, it will overflow through the reservoir overflow tube when the engine heats up. Once the level drops enough, it will still be high but will no longer overflow.
If you do notice that the coolant expansion tank overflows after being overfilled, check the coolant level again once the car has cooled to make sure that the coolant level hasn’t dropped too low.