Where does the file come from ? (I'm guessing you're talking about a CSV/XLS file)
If that comes from a system that you have control over, then get them to change the file (basically to unpivot the values)
If you don't have control over the file, then something like Alteryx or your own Python code needs to be used to pivot the data before you start using it in Tableau.
I think on another post the other day I mentioned that you would be facing this problem soon