What to do if you stole from someone and don't know how to pay them back?

Assalamulaikum, I stole a piece of stationery from a girl in my class when I was young (after puberty though), I have repented for my thievery, and regret it every time I remember, but I read the hadith that even deeds like jihad and martyrdom only expiates your rights to Allah swt, and not to the people, so a man who died as a martyr still went Hell because he stole a cloak from a war booty. (Muslim 1886) I am very scared because I no longer have the stolen items and don't know how to give back to the people I took things from. I think as a child I suffered from kleptomania after reading about it, but It was never diagnosed so I cant be sure. Jzk