Dark Souls for PC was a legendarily crappy port, and yet people continue to play it because a) it's an amazing game, and b) due to the hard work of modders. Joining the legions of benevolent Dark Souls mods is Input Customizer. As the name implies, it lets you customise inputs for gamepad, Steam controller and mouse and keyboard.
"[Input Customizer] uses an intuitive input system that allows the rebinding of every action to arbitrary combinations of keys or buttons on the controller, mouse or keyboard," the Nexus Mods description reads. "Although this can in part also be achieved with existing tools, DSIC is much more flexible and wraps it all up in an easy to use package, with additional functionality that is specially tailored to Dark Souls."
The work of modder Methanhydrat, it looks to be a pretty easy-to-use tool if the demonstration video embedded below is anything to go by. Note that you'll need to already have Durante's DSFix installed to get it up and running.