My assumption would be is that at some point they would be programmed with their route(s) for the day, but then there are other aspects like bringing sets of cars together etc.
What happens?
The units are coupled/uncoupled overnight in depots, particularly if one of the units is due for an Exam the following day or one has developed a fault.
At the start of service (from around 0430) onwards, trains are driven from the depot in Manual mode to the depot exits, known as Train Validation Areas, where the train will enter into Automatic operation. Trains will exit the depot in Automatic to their first station.
When entering into Automatic, they are assigned "run numbers" which identify the route they will be operating on and where on the schedule the train should be operating on. The schedule also identifies when trains should be returning to the depot, or for some trains, changing routes during the day.