I am not sure what you are asking about? Do you want to program nRF firmware in C#? If so, the answer is that Nordic have no support nor example for it.
Please try to add a bit more context to your questions in the future to make it easier to understand what you really want to know.
If you are asking for a C# library for performing a DFU over BLE, then there is no such library nor example. However, we do provide a Javascript implementation in pc-nrfconnect-ble (plugin for nRF Connect), as well as a python implementation in pc-nrfutil. (There is also libraries for iOS and Android).
