If you want to use the swing on the actual thermostat then use the custom DTH above to set it.
If you’re using a SmartApp like the 5-2 Day Thermostat or the Motion Sensor Thermostat with a remote sensor and define the swing in the app, then the app takes over the thermostat functionality and handles the swing internally. It can be as low as 0.1 I believe, essentially the actual thermostat is like a dumb terminal which used to turn the heat/cool on/off by the app until the desired temperature is reached on the remote sensor(s). You can find more details on each app on their respective pages.
There are lots of apps to choose from which provide different functionality, but in all cases where you’re using a remote sensor/swing the thermostat itself is turned into a terminal.