Roller appears to be fastened from top (as door was built)
Hello,
Our recommendation depends of what your patio door made of. If it's an Aluminum frame, then you will need to remove the bottom rail off the patio door to access that screw at the top of the roller housing. Take a look at the related videos on patio doors to assist you.
That does throw a rench in things since it would be difficult to install a screw from underneath a vinyl sliding door. Could you send us some more photos showing different views of the roller and of the patio door? It may also help to see the handle set used on your door.
If the head of the screw is rusted, you could try using WD-40 to loosen the screw and an EZ-Out extractor to remove it.