The free com0com tool will let you create a null modem connection between 2 com ports - so you can setup e.g. COM3 → COM4, set in SambaPOS COM4 for listening then send some data to COM3 and it will be picked up by SambaPOS on COM4.
If you have a look at the CHC source I posted on that topic, you can see the format that is being sent and you could send via command prompt echo whatever > COM3 or you could even just modify the program to just work to send test data to the COM port instead of interfacing with the USB caller ID device.
On another point, I notice your original post you were using “CID Show” as the device - that is a specific brand device, so it will be expecting that hardware to be connected. You want to use “Generic Modem” for your own implementation, it is compatible with most devices that send to a COM port.