-Go to https://www.uber.com/us/en/gift-cards/ and follow bellow :
Step1:Make sure you have the latest version of the Uber app.
Step2:Tap the menu icon and select Wallet.
Step3:Tap Add Payment Method or Redeem Gift Card.
Step4:Then tap Gift Card.
Step5:Enter your PIN/gift code (with no spaces).
Step6:Tap Add.