Low tire pressure, where to get nitrogen refill

What's everyone doing to refill their tires? With the cold weather I'm getting a low tire pressure warning. On top of that I don't know which one is low.

Read your owner's manual for instruction to access drivers center menu, TMPS display, for individual tire pressures. Nitrogen refilling can be done at most Discount Tires, thru the dealership or purchase your own system. All alternatives have a cost attached. 👍🇺🇸

Might be a dumb question, but what does nitrogen in your tires do for you vs air

Supposed to be less prone to temperature changes. So during the winter and summer it'll require less maintenance.