Get Signal on the App Store here.
Transfer Signal Data
In the blog post, Signal explains that you’ll need two iPhones: Your current (old) one and the new iPhone to which you want to transfer Signal data. Data transfers use a local connection and are encrypted end-to-end, like the rest of the app.
Signal generates a unique keypair for the encrypted device-to-device connection, and a MAC is embedded in the new device’s QR code so your existing device can verify the connection. The QR code itself does not include any sensitive information. […]
The new device verifies the integrity of the transferred data. If any errors are detected (for example, if the phones get too far apart and the connection dies), the process is simply aborted and you can try again later.
It requires downloading Signal on your new iPhone, and verifying your phone number. Once that is complete you’ll get a prompt asking if you want to transfer Signal data and message history. After you confirm it you’ll scan a special QR code and wait a minute or two.
The Signal app on your old device will then clear its data and you can start using it on your new iPhone immediately.