How to unlock sim after update

Feb 12, 2017
I updated my iphone the other night while I was sleeping and the phone was charging. Since then I have not received the usually prompt to 'unlock SIM'. I do have an unlocked phone. However, I am now unable to delete and edit songs in iTunes when I am connected to my laptop, and a message comes up about a locked SIM. Is there a way of unlocking my SIM, please?