If you accidentally miss your flight on United Airlines, there are a few things that you can do:

1. Contact United Airlines: As soon as you realise that you have missed your flight, you should contact United Airlines customer service. They may be able to help you with alternative flight options or provide you with a refund or credit of United Airline missed Flight.

2. Check your ticket: Some tickets may have flexible options or allow for changes or cancellations, but this depends on the type of ticket you purchased. Check your ticket or confirmation email for any information on this.

3. Consider your options: Depending on the circumstances, it may be possible to catch a later flight or find an alternative route to your destination. You can also consider purchasing a new ticket, but this will likely be more expensive than if you had booked in advance.

4. Be prepared to pay fees: If you need to make changes to your ticket, United Airlines may charge you fees. Be sure to check the airline's policies and fees before making any changes.

5. Arrive early for your new flight: If you are able to book a new flight, be sure to arrive early to the airport to allow for any unexpected delays or issues.

Overall, missing a flight can be stressful and inconvenient, but there are options available to help you reach your destination.