With airgap environments or where you’re unable to download the configuration for the WAN Edge device to establish DTLS tunnels back to SD-WAN Controllers you could use the Bootstrap option!

With the Bootstrap method, you can configure on SD-WAN Manager the pre-configuration and save this onto a USB Drive. When the WAN Edge is powered on it will then look for the Bootstrap file (ciscosdwan.cfg) with the initial configs to begin onboarding!