In my experience you can tell because they will be very lethargic and not as active as the others, not eating or drinking. Usually this indicates failure to thrive which is very very common to have one out of a group you get from the hatcheries. You can try giving it some electrolytes and scrambled egg but otherwise there’s not a whole lot (from my own experience) that you can do. Maybe someone has better advice for this but I’ve had chickens for some years now and know that sometimes you can lose one or two. Shoot I lost a whole batch I received from TS, once :-/ goodluck!