How can an anonymous collection of pamphlets, taken from a mosque years ago for reading and not yet returned, be given back?

It is not permissible to take books and Qur'ans endowed in the mosque for use outside of it. Whoever has done so must repent to Allah Almighty and return what they have taken. If it is damaged or lost, they must replace it. If they have forgotten the names of the lost books, they can seek assistance from the mosque's caretaker. If nothing can be ascertained, then it appears appropriate to purchase beneficial booklets with its value as an endowment, with an increase in number or value as a precaution and to absolve oneself.