iphone owner dies

One doesn't.

It is not possible for Apple or anyone else to recover or reset the lock screen passcode.

You may be able to gain access to any data stored in their iCloud account.

See this document: How to request access to a deceased family member's Apple accounts

If you know their Apple ID and Password there is "technically" a way to get access to the data. Though it would involve having to confirm if there was a backup of the device in iCloud or not first. If there is a known backup, you could in theory erase the device and then restore from the most recent backup, that would remove the passcode and put the data back on the device, but its all predicated on knowing the Apple ID and Password associated to the device. If you don't know that, you can't. There is no way around a passcode or activation lock. They are security services and workarounds or bypasses would defeat the purpose of it.