If you want to disable your SIM PIN, go to Settings - Cellular Data - SIM PIN. There you can enable, disable and change the PIN.
If you forgot the PIN, and entered a wrong one three times, you need the PUK. (If you enter a wrong PUK too many times, the SIM card is permanently locked and you have to contact your carrier for a new card.)
If you don't know/find the PUK or SIM, you'll need to contact your carrier.