If you’ve got your own gateway, then peek in its logs (or even easier: see the gateway’s Traffic page in TTN Console) to see if it’s trying to do an OTAA Join when powering up. If not, then you’re out of luck as you cannot use a pre-programmed ABP DevAddr.
Hello,
I was finally able to get a Ascoel Device CM868LRCB connected to TTN. The really provide a pre-configured AppKey and AppEui which has to be set in the TTN settings. It appears that the same for all Ascoel device AppEui doesn’t hurt.
There is a USB connector inside the device which gives you access to a serial console connection. There it is possible to change the AppEui and AppKey also to the TTN generated items. To do this you need to enter privileged user access and every device has different passwords which are normally provided with the device from the manufacture.