How to configure mdot to Join a LoRa network

Hello,

I want to configure my mdot to send messages to the LoRa network, so to do the Over The Air Activation (OTAA): I need to set the following parameters:
* DevEUI
* AppKey
* AppEUI

for the DevEUI it is ok it is on the device. But for the AppKey and AppEUI I am confused, how can I found them and set them in my mdot?

I can connect to a private LoRa network by setting the network id and password but how can I connect to a public LoRa network?

Thanks in advance for your help!