I'm confused by your terminology. I don't see anywhere in your code (or any reason in your description) why you are "... pass that into ColumA ..." Nor "(this is what I pass to the InputBox)" -- surely you are reading from the InputBox not passing anything into it.
If you mean that you are just wanting to compare a number(date?) that a user enters to the values(dates) in the first column of the spreadsheet and then extract the corresponding row, then why not either,
a) read the first column into MATLAB; determine which element (and hence row) corresponds to the value entered by the user; then use my previous code to read the specified row.
b) read everything from the specified sheet into MATLAB; then determine which row you want and extract it from the whole matrix that was read in.