What happens if you kill off all normal bacteria in the armpit? what type of infections does it cause? how can you restore the friendly bacteria

It will be ok: Very difficult to kill off all of the normal bacteria from your armpit. If if you were somehow able to do this, the normal bacteria from the rest of your body would get back into the armpit region. If were able to somehow get rid of all of the normal bacteria from your skin, bad bacteria could be staph Aureus. But in your case, the friendly bacteria from the rest of your body will seed the armpit.