What is the brand/model of your generic USB-IR reader?
Did it come with any documentation?
What application Software(s) does it recommend?
You will need a PC application software like Girder, Eventghost, etc.
You will also need to add a dummy device in the harmony, basically a device you don't have or don't use anymore, and configure the PC application Software to interpret the IR commands and map them to PC keyboard keys or functions.