Retirement tax questions

Form 8949, Part II (Long Term), Box E is checked [basis not reported to IRS], Line 1, Column (e) [Cost or other basis).  Because the basis of stock that I sold was not reported to the IRS by the brokerage firm (it was purchased before they started doing that), I entered the basis somewhere in TurboTax. I don't remember where.  The basis that I entered was automatically put in that Column (e).  I made a mistake and entered the wrong basis figure, so I need to correct my error it.  A lot of $$$ are involved. Right clicking on the incorrect figure, takes one to window that includes Data Source, but when I click on Data Source, nothing happens.  It should take me to the place in TurboTax where I entered the incorrect figure so that I can fix it there.  I cannot just overwrite the incorrect figure in Column (e) because one cannot electronically file a return that contains overwrites.  Today I spend over an hour on the telephone with TurboTax tech support.  The man was very nice, but he did not know how to fix the problem.  It should be a very simple question: Why does clicking on Data Source not work the way that it should? When he put me on hold for about the fifth time, he apparently disconnected the call and did not call me back.  This is  a MAJOR PROBLEM.  I need to know how to fix it. PLEASE HELP ME!