If you need to visit IIMB for a tour, it is best if you know a current student there or if you can connect with a faculty member on campus and discuss a common subject.
You should also avoid visiting during festivals because you will most likely be barred from all but the common areas and will be unable to find anyone who can tell you anything about the location.
When visiting any secured perimeter, it is more important to appear sincere, and presentable, and not faff around on your intentions or in general. Be open and honest about your intentions. The only issue is that there are too many people talking about being prospective students, and no one wants to take a security risk.
The security at IIM Bangalore is quite strict. Not anyone can visit the institution for a tour. But if you are genuinely interested in a campus tour here's what you can do.
Hope this helps.