Need to reformat mix of text and numbers

Hi - I am not an experienced Excel user so please excuse my lack of understanding of it! I have a shop which sells clothing and we have coded our stock with the following code A-1-1, A-1-2 etc going up to A-99-99 and beyond using letters of the alphabet. I cannot sort my list as where there is a single digit in the code, it needs a zero ie instead of A-1-1, I should have originally entered it as A-01-01. Is there a quick way of changing the whole list (which now runs to 3500 entries)? I don't understand formatting but I'm guessing there must be a quick way of doing this that doesn't involve manually changing each entry. thanks in advance for any help!