How to Turn off Stolen Device Protection without son's face ID (he's deceased).

My 9 year old passed away two years ago(would be 11 now). My daughter (his younger sister) has been using his phone for the last year as I never cancelled his line with my phone company. Anyway, Stolen device protection is on (how? Idk), and of course can't be turned off without face ID. But I can't do the face ID because...obviously. We've been using the passcode for everything this far but i finally have to courage to remove his apple ID from the phone and officially make it my daughter's phone. How do I turn off stolen device protection without Face ID? Please tell me there's some kind of work around or what can I do to make it hers