To use United Airlines travel credits, go to the United website or app and log into your account when booking a new flight. During the checkout process, you’ll have the option to apply travel credits. Enter the travel credit number you received from a previous cancellation or flight change. Make sure the credit is still valid, as they typically expire after 12 months. Once applied, the credit amount will be deducted from your total fare. If the credit doesn’t cover the full cost, you can pay the remaining balance with another payment method.