Most of the Ioniq EVs sold here in Jeju are the 'N' or lower trim. They do not have a battery heater. It never gets cold enough here that you would need it.
The battery heater is not controllable by the driver. If they have copied Kia with the Soul EV then the battery heater will come on somewhere around -20C automatically. You will need to read the Norwegian threads if you wish to understand how the car performs in weather this cold.
The pre-heating option warms the inside of the car, not the battery. The car needs to be plugged in. If you set it to +20C thirty minutes before you leave then the car will be warm when you get in. This makes it much more comfortable when you get in, and saves energy from the traction battery.
Here's a graph from the Soul EV that shows the power requirement in kW needed to pre-heat the cabin.
The codes for using Torque Pro can be found by clicking the link in the website icon under my user name on the left.