Don't learn anything new
Anything you haven't learned by the night before, you will not learn well enough tonight to use it tomorrow — and trying will just make you anxious about how much you 'still don't know'.
What to actually do instead
Skim your formula sheet once, out loud, to refresh the ones you already know rather than trying to memorise new ones cold.
Lay out everything you need for tomorrow — calculator (fresh batteries), ID, stationery, water — so tomorrow morning has one less thing to think about.
Do 15–20 minutes of easy, confidence-building questions you already know how to do. This is about warming up your brain, not testing it.
Sleep is not optional
A tired brain performs worse at method marks and careless-mistake avoidance than a rested brain that knows slightly less. Aim for a real night's sleep — this is one of the highest-leverage things you can do the night before.