My Venus Flytraps here in New Mexico usually don't enter dormancy until the last half of November. I keep them fairly warm to extend the growing season, and gradually lower the temperature (I have a heater and thermostat in the greenhouse) to where it is fairly cool for a person (but not necessarily for a plant) at night.
Just allow your plant to experience slightly cooler temperatures along with the diminishing daylight hours. If your plant is on a window sill, and if the window is not an insulated one, the cool air falling from the inside surface of the glass will cool the plant some. If that's not enough, you can close the curtain in the evening with the plant between the curtain and the glass, or tape a plastic sheet to the window frame with the plant between it and the glass. You will notice the plant growing more and more slowly until it barely grows at all. Quite a few leaves may die. At that point, you could move it to the place it will spend its dormancy.
Just some suggestions. Good luck.