Damus settings should have somewhere you can get your private key (nsec). Store this somewhere safe, like a password manager that stores your passwords encrypted. I like Keepass or Bitwarden.

You can paste this nsec into other Nostr apps to log in. Best practice would be to use a signer application, rather than pasting your nsec into every app you want to try. That's a good way to have your private key compromised. However, iOS doesn't have a signer app available yet.