How to reset iPhone 8 password and iCloud email address without access?

Hiya I set my granddaughters iPhone 8 up a long time ago but have since forgotten the password and the password for her iCloud email address. When I try to recover her password a code is sent to my phone. I enter the code on her phone but it then it says something about the link to reset her password to her iCloud email address but obviously we can access it because we have forgotten the password for that to. Can someone please help me sort my granddaughter’s password out as she can not download any games or apps.