and here is how to use live focus after installing it.........

open camera app and start video rec. and now tap screen(anywhere if it is not full screen) >now on the top left corner (yes the status bar where the battery indicator etc. is shown) tap there and you will see a new menu or you may call icon(this red icon is live focus icon) tap the icon and here you will see all functions of live focus(touch arrow button for more functions)

good luck
BTW there is a "Thanks!" button to press instead of saying thanks.