1. Contact the bank: call your bank's customer service number and ask how to lock the secondary card. Usually, the bank will ask you to provide some basic information to verify your identity, such as card number, cardholder's name, ID number, etc. After verification, you can ask the bank to lock the secondary card.
2. Use online banking: If your bank provides online banking services, you can also lock the secondary card in online banking. The specific steps may vary from bank to bank. Generally, you need to log in to your online banking account, select the secondary card to be locked in the options of "Credit Card Management" or "Secondary Card Management", and follow the prompts.
No matter which method you use to lock the secondary card, it is recommended that you read the relevant operating instructions and precautions in advance to avoid unnecessary losses caused by misoperation. At the same time, if you need to use the secondary card again, you can contact the bank and unlock it accordingly.