where can I find when had the user made changes to the account hierarchy

  hello everyone

I am new to the oracle e-business suite

And what I am going to do is  to audit our oracle e-business suite system

my question is I don't know where could I found the record which had record when did the user have

made changes to the account hierachy

I thought it would be in the log file, but there is too much log files to find out

so it took me a long time and I still can't find out

And that's the reason I came hear for help

can anyone teach me where could I find the information I need ?