I found iphone 13 pro max how can i unlock??

Sorry, but without proof of ownership nobody can unlock this device to use it.

You should return it to a Lost&Found next to your place since the owner is probably looking for it.

Or follow these steps to return it:

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copied from: Return a lost, locked iPhone - Apple Support

Hello ~ Follow the instructions on the iPhone screen. You will not be able to use the device and it has been reported stolen.

~Katana-San~