1. Ask the flight attendant on the train: You can ask the flight attendant on the train if you can make an invoice, indicating that you have accidentally checked the option that you don't need an invoice. If the waiter can help with the invoice, the problem can be solved.

2. Contact the high-speed rail service department: If it cannot be solved on the train, you can contact the high-speed rail service department to explain the situation, apply for an invoice, and provide your own order information and other necessary information. Generally speaking, the high-speed rail service department will try its best to help customers solve problems.

3. Consult the merchant's customer service: If you have left the high-speed rail, you can also contact the merchant's customer service to inquire whether you can issue an invoice and provide your own order information and other necessary information. Merchant customer service can further coordinate and solve the problem.