how to unlock sims

What exactly are you asking? Do you mean the iPhone is locked to a carrier and you want to see about unlocking that, or the SIM is locked and asking for a code. If you are talking about locked to a carrier, you must check with the carrier the device is locked to and see if they provide unlocking services and if you qualify. If you are referring to an unlock code for the SIM, you need to contact the carrier the SIM came from, they provide those codes.

if you have unlocked your phone for use with another carrier, follow this link

How to unlock your iPhone for use with another carrier - Apple Support --https://support.apple.com/en-ca/HT201328https://support.apple.com/en-ca/HT201328

iOS: Understanding the SIM PIN - Apple Support -- https://support.apple.com/en-ca/HT201529

iOS: Understanding the SIM PIN

I don't quite understand your question, is this something you're referring to?

Personal Unlocking Key (PUK)

If you enter the PIN incorrectly three times, you may need to enter a Personal Unlocking Key (PUK) to enable your SIM card again. Refer to the SIM card documentation or contact your carrier.

Note: Entering an incorrect PUK code too many times will result in the SIM becoming permanently locked. If this occurs, you will need to contact your carrier for a replacement SIM card.