Turn on rear window defogger, give few seconds and touch the side mirror. They will be heated up and warm. You can easily tell there is a heating element behind them
A guy posted about only replace the glass / mirror part of it in a group on facebook and another guy replied that you have to probably replace whole side mirrors as they are heated. He himself found it couple of days ago. I searched in manual downloaded from main Hyundai site and it is written in it.
