Soccerdad1995, you should have a receipt in your email. Reply to it and say the driver misled you into handing over $20 cash. Ask Uber to refund $20 to your credit card.
Uber is a cashless experience. Tip is not customary for UberX/Black/SUV/LUX/RUSH/EATS/anything except UberTAXI. For UberTAXI, Uber will add 20% of your meter in a separate line item to your fare. That's the tip.