How to unlock my iPhone from carrier lock?

Are you sure that the phone is not Activation Locked? If it is, you need to have your friend follow these instructions:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

Otherwise, your friend needs to contact the carrier that is locked to the phone and ask the carrier to remove the lock on the phone.

Only the carrier it is locked to can unlock it.

As a rule, they will only do so for a current or former customer in good standing.

Have the friend you got it from contact the carrier and request an unlock.

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

Only the carrier can unlock the phone, so your friend will need to contact the carrier and ask them to unlock the phone.