If it is a China Merchants Bank credit card, the principal cardholder can apply for the supplementary card through the following channels: Path 1: Apply for the principal card and supplementary card simultaneously. Please check the supplementary card when applying. Method 2: The main cardholder applies for a supplementary card for relatives. 1. Apply for a card online: The principal cardholder completes the application according to the steps on the website. 2. To apply for a card at a China Merchants Bank branch: the principal cardholder must bring the original identity document of the supplementary cardholder, and the supplementary cardholder does not need to go together.