3 office choices

Dear Community and coaches,

I have a Q regarding the application process at MBBs (in particular Bain, BCG). When you have chosen three offices and you get rejected from the first office choice, what happens to the application, Is the application sent to the second office of choice automatically or you need to do something for that? 

2nd Q, whether rejection from one office affects the application process in other offices?

3rd Q, What about the cover letter, D you need to add another cover letter for that office?

4th Q) how the referral role come to play if the process is passed to the 2nd office automatically?

Thanks for sharing ur ideas