Here is a video or follow the steps below.
Tap "Settings"

Tap "Geofence"

Tap the slider next to "Guard" to turn blue

Select "Confirm"
Guard has been enabled
To disable, tap slider again, and select confirm when prompted
Here is a video or follow the steps below.
Tap "Settings"

Tap "Geofence"

Tap the slider next to "Guard" to turn blue

Select "Confirm"
Guard has been enabled
To disable, tap slider again, and select confirm when prompted