I was having problems with one of the fobs and thought it needed a new battery. I replaced the battery and as I didn't know which of the 4 fobs it was, tried to set it as a new fob number 5. I've obviously done something wrong as one of the other fobs is notlarming or disarming the system. How do I find out which number each fob is, the numbers have come off the back? And how do I clear the fob where I've replaced the battery so I can install it as number 5?