United Airlines' cancellation policy enables passengers to cancel or modify their flights, with fees mainly depending on the fare type and timing. A credit voucher is provided for non-refundable tickets. Flexible tickets allow free changes or cancellations within 24 hours of booking.
https://www.flightslineup.com/....blog/united-airlines

Alaska Airlines Change Flight enables you to change your flight with minimal effort, making it easy to change your travel plans as needed. You can change your flight details through their website or mobile application, or call customer service to help update your flight information.
https://www.flightslineup.com/....blog/alaska-airlines