Even if you pay for your trip with a bank card, you can still leave a tip for the driver:
To set a single tip rate for all your trips, go to the Tips section in the app menu.
To set or change the tip amount for one trip, use the form that opens in the app at the end of your trip.
A tip is withdrawn automatically if you give a positive rating to the driver within 30 minutes of the end of your trip and tap Done (or just close the rating screen).
If you give the trip a positive rating but don't tap Done (or don't close the rating screen), the tip amount will be reserved on your card for 24 hours. The tip amount may change during that time. The amount indicated will be withdrawn in 24 hours.