it's not hidden. it's in your owner's manual. there's a button with ESC on it. hold it down until you get an alert and this icon
View attachment 54094
shows up on your dash (i pulled this from the internet. can't remember if it says "OFF" on the dash but you'll get the image)
edit: i own a 2019 and i also don't have heated seats. the button's still there. it's just flanked by blank buttons where the heated seat buttons should be.