GranolaTTS

Go to the menu, select systems - Servicing & checks - tire pressure monitoring system - store tire pressures -  yes store now & the light will go from the dash. 
Obviously, make sure you check all the tires are inflated to the correct pressure first... & Pump them up to the correct pressure. The cold often causes TPMS issues as the density of warm air is less in comparison to cold air. Around 1/2 PSI per 10 degrees in temperature. 
Or you could have a puncture or slow puncture. So best to keep an eye on the pressures after you reset, but almost every time it has happened to me it's just the car crying about nothing. It is not unusual for tires to naturally lose 1.3 PSI per month as air gets through the rubber via permeation. 
Pressures will be in Manual or can be found online...
Air can leak from the Tyre, valve, and rim if it's cracked or corroded around the seal. But I would place my bets on a slight pressure drop or a slow puncture.  Best to check the Tread condition and for any visible damage to each tyre while you're at it also.