Welcome to the community!
What are you attempting to do? As far as I am aware, the Fido SIMs do have a default PIN: 3436 (see here and here). However, the function to enable a SIM lock would be on your phone (see Android vs iOS).
If you weren't aware, if you make 3 unsuccessful attempts at unlocking your SIM card, you will need your PIN unlocking code (PUK). You can get your PUK via your My Account --> Usage & Services --> Mobile (or Phone Number if multiple lines). From there, you would need to click Retrieve PUK Code under Quick actions. If you are not immediately provided with the Usage & Services heading, you might need to select Profile & Settings first.
Hope this helps 😀