Maybe you can program RAK8212 via BLE DFU.
There is a demo of RAK8212 BLE DFU, you can refer to it. https://github.com/RAKWireless/RAK8212-itracker-firmware-based-on-nRF5SDK15.0.0-with-DFU

BTW, you can only upgrade the application of RAK8212 via cellular, like GPRS, NB-IoT, Cat M1. If you want it, please see this open source project: https://github.com/RAKWireless/RUI_itracker_platform_firmware