It takes a few attempts to figure this out.

If you're leaving from CHI where the train originates, the primary interest would be in checking arrivals at the destination, let's say Fort Worth (FTW). In that case, all you need to do is insert the train number, and "FTW" in the arrival box, along with the date of arrival.

Even if you're departing from an intermediate location, like St. Louis (STL), you can use the "arrival" check to see how the train did there on that date.

The only thing to watch out for is when the train operates over more than one day. You will want to be sure that you have information for the right day.