If these devices are in AxM, then you can add a new MDM server in AxM, add it to your Jamf instance (Settings -> Automated Device Enrollment). In the new prestage, set the new Automated Device Enrollment instance as the default for that prestage. Then you can select the devices in AxM (if you have the serial numbers in a csv, you can copy and paste the serials into the search field in AxM), edit MDM server and select the new MDM server. The devices will move in AxM, then when Jamf syncs with AxM, the devices will be reassigned from their current prestage to the new one. I used this method to move almost 20k devices.