If you find that the micro:bit is not letting you update it after using one of the apps, it might be because the last Bluetooth flashing process was unsuccessful. 

This can cause the micro:bit to appear unresponsive, with a blank screen and not able to enter pairing mode.

If this happens, 

  1. Hold down reset and  connect the micro:bit to a computer via USB to  Enter MAINTENANCE mode.
  2. Flash the micro:bit with the latest firmware
  3.  'forget' the micro:bit, in the Bluetooth settings on your mobile device and pair it again.

It should now work again with the app.