Conducting research at my alma mater I'm thinking about conducting a research at a specific division of the university from which I received my PhD. I had a negative experience while I was there. And I keep hearing that many other students there are going through horrific experiences of abuse. I'd like to conduct a study case and perhaps better understand what's going on there. I know many other institutions have similar problems, but, as I said, I'd like to do a case study and then perhaps go from there to researching other institutions.The problem is that I don't work there, I'm just part of their alumni. I work at a different university. So, basically, this would be an independent study. My question is, given that this is not a dissertation proposal, can I simply complete the IRB form as an independent researcher? Or do I have to write a whole proposal? I know each university is different, but can someone give me an idea of how this works? I'm new to this idea. Thank you.
Since the other university is actually the subject of your study, then I think that the IRB of your current university is the better place to judge it. It avoids a conflict of interest within the other university. 

Your former colleague at the other university probably shouldn't be a co-researcher, but could be integrated into the study in another way; say as a source of information. This lets them, also, avoid a conflict. 

Proposing it to the Dean at that university may also be problematic. Your "want to help them fix the problem" will very possibly not be well received. You might get quite a lot of blowback. 

If they recognize the problem on their own and come to you as a consultant, then it is a different story. Otherwise you will come across as an unwelcome outsider and a disgruntled alum. 

I won't recommend against your study, but I think that you should keep it as independent of the other university's administration as possible.