I wanted to clean the iPhone S6 of my daughter but now it is not possible and it asks for a Beperkingencode

I wanted to clean the IPhone of my daughter a 6S but now it is not possible and it asks for a Beperkingencode. Did not even know we put it in? Tried some regular simple codes but that does not work. Does anybody know how to get this off so I can clean the IPhone for my other family member to use. My grand mother! Thanks Floor

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