Change Apple id login on children protected device

My iphone 7 died.

I am using the iphone from my (minor) child. This iphone has her apple id logged in. Her apple id is a child profile and has a lot of limitations that I had configured from my "parent" iphone when it was still working.

I can't sign out of her child apple id (I had restricted this feature) and I can't change the limitations if I can't access my apple id profile. I can't login with my parent Apple id on the device to be able to unlock... And this is not something that can be configured from a PC.

Help please! any suggestion?