Set up a backup way to sign in
Add a second sign-in method so you can still reach your account if you switch phones.
Open the More menu from the tray, tap Settings, then Security, and find Backup sign-in. The row tells you what it can add, for example "Add Google as a second way to reach your account."
Tap it, and your phone opens that provider's sign-in sheet. Choose the account you want to add and confirm. Carlo then shows Done, and from that point either method reaches this same account.
What you are offered depends on how you signed in. If you used Apple, Carlo offers Google, which is the one to do if you use Apple's private email relay, since it gives you a real second way in. If you used Google on an iPhone, Carlo offers Apple. If both are already connected the row simply reads that you are covered, and there is nothing to do. On Android, signing in with Google leaves no second method to add at the moment, so your recovery code is what protects you there.
Be clear about what this does and does not do, because the names invite confusion. Linking gives you a second way to sign in. It does not unlock your data on a new phone, and for that you still need your 12-word recovery code. Without that code your data stays locked even after you have signed back in successfully, so keep it somewhere safe.
If you see a message that the account is already connected to a different Carlo account, you have most likely set up a second account with it by mistake. Send feedback and we can help sort it out.