How to cancel this repeating alarm?

Call cancel() on AlarmManager with an equivalent PendingIntent to the one you used with setRepeating():

Intent intent = new Intent(this, AlarmReceive.class);
PendingIntent sender = PendingIntent.getBroadcast(this, 0, intent, 0);
AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);

alarmManager.cancel(sender);