Move Carlo to a new device
Sign in on the new phone and your key usually loads by itself. Your recovery code is the fallback.
Open Carlo on the new phone and sign in with the same account you used before, whether that is Google, Apple, or email. Your transaction history loads from the server automatically.
Your encryption key usually comes across on its own. Carlo keeps it in your cloud storage, iCloud Drive on iPhone and a private app area of Google Drive on Android, so signing in lets Carlo find it with nothing extra for you to do. On Android you will not see a file, which is intentional and the same as on iPhone. Between two iPhones on the same Apple ID with iCloud Drive on, it usually takes a few seconds.
If the key cannot be loaded, Carlo prompts you, and this is where your 12-word recovery code comes in. If you still have your old phone, open Settings → Security → Recovery code there and save or copy it, or tap Export PDF for your own copy. Then enter it on the new phone, by scanning the QR or typing the words.
Moving between an iPhone and an Android phone is the case where you will definitely need it, because each platform stores the key in its own cloud and neither can reach the other.
If you have lost the old phone, sign in on the new one and let Carlo try the cloud first. If that fails you will need your recovery code, and if you never saved it and cloud storage is not available, the data cannot be recovered. That is the honest limit of end-to-end encryption, and the reason to keep a copy somewhere.
One consequence of the convenience worth understanding: because your key loads automatically from your Apple or Google account, anyone who can sign into that account on a new device can load your data too. Protect it with a strong password and two-factor authentication, and on iPhone consider turning on Advanced Data Protection for iCloud.