[joecool1029]

I think you need the old device in hand to do it. If you wipe the device and restore from a backup, there's no way to transfer the history. There's some new cloud backup feature in Signal Android Beta, but this wouldn't help on an iPhone.

[Zak]

There's an option for a password-protected backup to the local filesystem. Of course you need to copy that backup to somewhere else if you want to be able to restore it without the old phone.