The process to do this on Delta is super easy.
On your old device (with your data) go into Settings -> Transfer data -> Transfer to other device. This will open the camera to scan a QR code.
Install Delta on your new device and go into it's Settings -> Transfer data -> Transfer to this device. This will display a QR code that is valid for only 10 minutes.
After you scan the QR code, the app will ask for confirmation.
Please note that transferring will move ALL the data from this device to another i.e. the data will be removed from the old device. If there was any existing data on the new device it will be removed as well and overwritten by the data you are transferring. This is irreversible!
If instead you wanted to sync data between your devices check the article on device syncing.