Transmission fluid?

My 2018 Hyundai Elantra has 230k miles and has never had its transmission fluid changed. Now if it doesn’t sit for 5-10 minutes before driving it won’t shift at all until it’s warmer. A guy I work with builds race cars and told me not to mess with it because of the mileage but I’d rather ask people who have running cars. So should I change it or just add to it? Any advice would be appreciated!