You can delete your Nerdi account from inside the app. You do not need to contact anyone.
Your account, your saved papers and reading positions, your notes and collections, the papers you dismissed, your interests, and the usage records tied to your account. This is immediate and cannot be undone.
The copy of your library held on your own device is erased at the same time.
Usage records created while you were signed out carry no account identifier, so there is nothing connecting them to you and no way to identify them as yours. Crash reports contain no account identifier either.
Deleting your account does not cancel Nerdi Plus. Apple bills the subscription, so cancel it in iPhone Settings → your name → Subscriptions, or it keeps renewing. RevenueCat, which confirms subscriptions for Nerdi, also keeps its record of your purchases; email korayozcan33@gmail.com to have it removed.
Email korayozcan33@gmail.com from the address associated with your account and ask for deletion.