1. Contact the customer service of the National Digital Library: you can contact the customer service team of the National Digital Library by calling customer service, sending emails, online customer service, etc. They will provide you with specific guidance and help you regain the QR code of your e-reader card.
2. Log in to the library official website: If you still remember your library account number and password, you can try to log in to the National Digital Library official website or the official mobile phone application. On the user's personal information page, you may find information about the e-reader card, including the QR code. You can try to download or take screenshots to save the QR code and use it if necessary.
3. Consult the user manual or help file: If the National Digital Library provides relevant user manuals or help files, you can find the instructions for using the QR code. These materials can usually be found in the help center in official website or the document download area of the library.
If the above methods still fail to solve your problem, I suggest you directly contact the customer service team of the National Digital Library to describe your situation in detail and seek their further help and guidance. They will have more accurate and specific suggestions to help you retrieve or regain the QR code of your e-reader card.