As of today, it's not possible to change the Picnic card PIN.
The PIN is automatically set by the system when the physical card is activated and, for now, cannot be customized or changed afterwards.
How to View the Card PIN
If you forgot the PIN or haven't memorized it yet, you can check it through the app:
Open the Picnic app and log in with your email.
Tap on “View PIN”.
Follow the on-screen security instructions to view it.
Whenever needed, you can repeat this process to check the PIN.
What If Someone Saw My PIN?
If you suspect that someone else knows your card PIN:
Freeze the card through the app (temporary or permanent block).
Report the loss (to automatically cancel the card)
Canceling will allow you to request another physical card.
Summary
It's not possible to change the Picnic card PIN at this time.
You can check the current PIN whenever needed, directly through the app.
If you suspect a PIN leak, cancel the card and request another.
See Also
How to Activate the Physical Card and View the PIN