You can modify it directly on the mobile client of the corresponding bank. The following is a demonstration of the modification of the Agricultural Bank of China. The method is as follows:

1. Open the remaining Agricultural Bank of China mobile client.

2. Next enter the client and log in to your bank account.

3. Then select "My Account" as indicated by the arrow in the picture below.

4. Enter the My Account page and select the setting option indicated by the arrow in the upper right corner as shown below.

5. Next, select "Change Debit Card PIN" indicated by the arrow in the list.

6. Then enter the password you want to change according to the prompts on the page, and click "OK".