Inherited iPhone from deceased father-in-law - how to remove apple id from iphone

Good day,

we inherited an iPhone from the deceased father of my partner.

His apple id and password are on the phone. We do not know the password....

We would like to use the iPhone, but it is basically 'blocked' as we cannot even change the time(zone).

What can I do?

We can supply the Death Certificate, if need be, to verify the case.