How to create customized software to program boards via bluetooth on nRF Connect

Hi, I'd like to add that "BLE capabilities for nRF Connect" to my customized software in the dongle, is there an example code or template which I can add to my customized code such that it can do that? Because when I tried using the dfu sample codes that come with the SDK 17.1.0, I was stilled asked to program the device to something else.