Nostr is a protocol, not an app. Each Nostr client app has a different way of deleting the data you wanted to keep. 😜

What app? Some store them as Nostr events so they are just there when you sign in. Tell your dev to support the bookmarks event, then they are saved to relays 👍 https://nostr-nips.com/nip-51 https://nostrbook.dev/kinds/30003