The 9500 is the battery operated switch, right?
In that case, you don’t need to directly associate it the way Cooper describes.
Both devices are Z wave and so both can independently be controlled by smart things. So you can just have the master respond to activity on the 9500 the same way you could have it respond to a handheld minimote or a zigbee switch on another floor or a contact sensor in the garage or whatever.
Essentially instead of the 9500 talking directly to the master, it will talk to the hub and then the hub will send the message to the master.
There are other master/auxiliary pairs from various brands where the auxiliary is not a network device and can communicate only to the master, not to the hub. In that case the process is different. But as long as the auxiliary is recognized by the Hub as a networked device, Smartthings offers you a much wider set of options.