How do I unlock my iPhone 14 Pro Max for use with another carrier?

You can't. No Pakistani carrier offers unlocking for iPhones.

Apple won't remove carrier locks unless they accidentally replaced an unlocked phone with a locked one.

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You have to contact the carrier the phone is locked to and see if the phone qualified to be unlocked, which could require paying off any balance owed on the phone. Apple cannot unlock a carrier locked phone. ONLY the carrier can do that.