The steps to get the code is in the guide itself. It's crossed out in the Computer A section (it's in the 3rd post btw)
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If you mean the safe inside the computer room, then unfortunately i didn't find anything myself and there are no possible way to access it either, as far as i remember. If you meant the Jay's safe, then the code is in the third post, where there are a bunch of capitalized letters, symbols and numbers