Erasing previous Apple ID from iPhone without the password

I lent a friend my iPhoneSE some time ago and they listed an apple ID even thought they don't have one or can not recall setting one up. This person is no longer with us and I have the phone back.I am trying to do a factory reset but it wants the persons password, of which there not one. It will not allow me to turn off Find my Phone so I can not do a factor reset. It also will not allow me to add my apple ID (I think this could be because I had previously used that on this phone before) either way I can't do anything with the phone. Can anyone help with how I can change the apple ID or turn off Find my Phone so I can do a reset?