TI SensorTag firmware Update through OAD(over-the air ) in android
It's not available because you have an old version of the TI firmware in your SensorTag. Some months ago they added the "Connection control service" to the SensorTag firmware to enable OAD with Android. If your firmware is not recent, it has the OAD Service but not the Connection Control Service, so you'll have to use iOS to to OAD.