In the astrology room, there is a grid next to the map and there are coordinates. You'll need to add up the first numbers in each coordination and then separately add up the second ones. When you put the two results together (example: If you would have the numbers 244 and 254, it would look like this: 244254. 24 = the locker number, 4254 = the code), you get a locker number 23 and a four-digit code.
Hope this helped!^^ Sorry if you can't understand, english isn't my first language and I am not very good at explaining, too. ^^''