This is the 17133rd most frequent Turkish word.
çöpte
"In the trash" or "in the garbage."
In this sentence, 'çöpte' indicates the location of the books, namely 'in the trash'.
Kitaplarını çöpte buldum.
I found your books in the trash.
Here, 'çöpte' is used to describe the current state or presence of the papers in the trash.
Kağıtlar çöpte olduğuna göre geri dönüşebilir.
The papers are in the trash, so they can be recycled.
'Çöpte' expresses the place where the action of searching is taking place, i.e., in the trash.