When the supplementary card is lost, contact the bank promptly to handle the loss report and replacement procedures, provide accurate information and pay the loss reporting fee. The bank will send a new supplementary card, which may require additional documentation. Ensure account security and avoid financial losses.

When the supplementary card is lost, the steps to replace the supplementary card are as follows:

1. The first step is to contact the card-issuing bank as soon as possible to notify the loss of the supplementary card. You can call the bank's customer service hotline or submit a lost card report on the bank's online banking platform.

2. When reporting to bank customer service or online, you need to provide relevant identity information, such as primary card number, secondary card number, cardholder name, ID number, etc. Make sure you provide accurate information so the bank can accurately identify your account.

3. The bank will ask you to fill in a loss report application form, which must indicate the reason and specific circumstances of the loss of the secondary card. After completing the form, it needs to be signed and submitted to the bank.

4. The bank may require payment of certain loss reporting fees. The amount of the fee will vary according to the bank's policy. You can consult the bank's customer service or review relevant information when declaring.

5. The bank will record the loss report information in the system and send you a new supplementary card. Normally, you will receive a letter containing the new supplementary card, which needs to be signed for confirmation upon receipt.

6. During the process of applying for a replacement card, you may need to provide some additional documents or certificates, such as identity certificate, household register, loss report, etc. Specific requirements may vary depending on bank policies. You can consult bank customer service for accurate information when declaring.

Legal basis:

Measures for the supervision and management of credit card business of commercial banks:

Chapter 4 Management of Card Issuance Business Article 63 The issuing bank shall provide Card replacement service provides card replacement for cardholders who meet the expiration conditions for card replacement. Exceptions will be made if the cardholder proposes not to renew the card upon expiration, not to change the card, or to cancel the account. \nFor credit card accounts that have not been activated by the cardholder within the validity period of the credit card, the card-issuing bank shall not provide card replacement services upon expiration.

When the supplementary card is lost, it is most important to contact the card-issuing bank in a timely manner and go through the loss reporting and replacement procedures in accordance with the bank's requirements. This can avoid unnecessary financial losses and ensure the safety of your account. At the same time, you should also closely monitor the transaction records of your supplementary card account to protect the security of your card and personal information. Following the bank's security recommendations, such as changing your password regularly and not disclosing your card and password to others, can better protect the security of your funds.