How do I disable SIM lock on iPhone?

If the SIM is “locked” with an unknown PIN, contact your carrier for assistance.

Use a SIM PIN for your iPhone or iPad - Apple Support

If your phone is “carrier locked” so that it will not use the SIM of your chosen carrier; your options are quite limited.

Only the locking carrier can unlock the phone, but if you’re not one of their subscribers … they have no economic incentive to do so.

How to unlock your iPhone for use with a different carrier - Apple Support

See this document about a locked SIM message --> Use a SIM PIN for your iPhone or iPad - Apple Support

If your SIM is locked then you will need the code used to lock it. If you do not know it, go to your carrier and ask for a new SIM.