That device is a battery powered handheld or wallmount remote, you can’t actuate it from the system. That is, the system can’t tell the device to turn on or off. That’s why it’s not showing up.
So instead, you have to create a smartlighting automation that controls the same bulbs that the lightify switch does.
This is true of most of the devices that smartthings calls a “button controller.” The hub will be told when someone physically presses a button, but you can’t write an automation that essentially tells the device to press the button, it’s just not how most of those battery-operated devices work.
The main difference between this and a regular wired switch is that a wired switch is always listening to the network, so it’s easy to send it an “on” command.
Most of The battery operated devices actually sleep most of the time in order to extend battery life. When you physically press a button on the device, you wake it up, and then it can send a message to the hub. But if you try to trigger it by sending a message from the hub and it’s asleep, the message will be lost. So most of these devices don’t accept incoming messages unless they are specifically put into a configuration mode.