Sorry, I’m confused by the question. The iBeacon itself is always on.
When Using beacons for presence, most people create a virtual presence sensor (abbreviated VPS) which also has the “switch” capability so you can turn it on and off in SmartThings.
So you turn the VPS on when you are in range of the beacon and off when you leave the region. This causes the VPS to register to ST as “Home” or “away.” But the beacon itself is always on.
This is covered in the presence FAQ. See post 5 for a link to the VPS code.