How to unlock iphone because the owner of this is died?

If you have any relation to the deceased owner, take the device to an Apple Store with proof of purchase, proof of death and also docs that relate you to that person so Apple can help you unlock it.

Call Apple Support first Contact Apple for support and service - Apple Support and check with them how to proceed to get everything right, Ok?

Click or tap > How to request access to a deceased family member's Apple accounts - Apple Support

Note that even Apple cannot gain access to a device, with intact data, if the screen lock passcode is not known.