Proceed as follows:
1. In the app, select "Trips" in the lower menu bar.
2. Choose first the month, then the day and finally the ride.
3. You get to a menu where you see the trip on the map above and the details below. Directly below the map on the right side, it has a symbol, which looks like an arrow pointing upwards or a bunch of keys.
4. Click on this symbol and then you can choose between three trip categories: "Private", "Commuting" or "Work".