No need to really do anything. In fact it's usually best to take a 'hands off' approach. The hen should sit tight and stop taking bio breaks. (If she gets off for a min, don't panic. Hen usually knows best.) You may catch her "talking" to her eggs - encouraging them to hatch. You may also hear 'peeping' from chicks or even pipped eggs. There's really nothing to "see" until the mom leaves the nest and the chicks follow. Hatching all the eggs often takes 24 hrs, but it could also be drawn out if the temps were not consistent. The hen will stay in the nest until either all the eggs hatch and the chicks dry OR until she feels, the last egg will not hatch and it's time to move on. (Candle any remaining eggs for signs of life because sometimes they can be hatched.)
Since it is below freezing outside, the eggs may take a couple extra days. They may hatch on Sunday or they may hatch on Tuesday. Don't freak out. Be patient. In the summer, my hen Cookie always runs hot. Her eggs hatch in 19 days - not 21. So the 1st time she did a winter hatch, I was ready day 19 but they didn't hatch until day 22.
Good luck and enjoy the fun!
edit to add: The only thing you may need to do is clean up a broody poop. My MaiMai just pooped & it smelled horrible. Although the poop didn't touch the eggs, it was close enough and I didn't want a newly hatched chick crawling through it.