Open WhatsApp and select "More Options" from the Menu which is available at the top of the right corner.
Click on the "Payment" option, followed by the selection of the bank account
Click on the "Change UPI PIN" or "Forgot UPI PIN" option to change or enter the new PIN
If you forgot your UPI PIN then press the "Continue " tab after selecting a relevant option and your banking information asked for change here
It will not take you more time to update the banking information and you can set up the new PIN instantly .