The video at the top of the thread could still be somewhat helpful, even for a DXs. You really can't change any settings for a DXs (and don't want to if it came with a plane, or else it may not work with the plane.)
First you have to bind the DXs to the USB wireless receiver. That's done by holding down the button on the USB receiver while you plug it into a USB port. The light inside the USB receiver will start flashing. Then bind the DXs by holding down the button on that while turning it on. After a few seconds, the light on the USB receiver should stay on solid.
In RealFlight, you'll have to calibrate the controller as shown in the video. The controls may not be correct, so you'll need to select the proper Controller Profile. There's one called "Spektrum Receiver (DXS)" that will probably be best suited for your DXs, especially if it came with an airplane.
If none of that is helpful, please explain where you're getting stuck and be more specific about what's not working.