I have buy an iPhone 13 pro max from USA i brought it in pakistan but it's sim locked what should I do to make it unlocked

What retailer did you buy it from?

If you bought it from anyone other than directly from Apple, for example, Best Buy, Target, Walmart, etc, you did NOT buy an unlocked phone.

It can ONLY be activated using a US carrier. When it is activated it will lock to the carrier used to activate it. ONLY the carrier it is locked to can unlock it.

Did you activate it in the US at all? If so, contact the carrier you activated it on. They are the only ones who can unlock it.

Where, exactly, did you buy it?

The ONLY source for unlocked iPhones in the US is directly from Apple.

iPhones sold by other retailers will lock to the first US carrier used. Only the carrier it is locked to can unlock it.

If you are not a current customer in good standing of the US carrier it is locked to, it's going to be difficult at best to get it unlocked.

Some carriers do not offer unlocking at all.