from the file/open, change file type to "all files", then
select the file.
You could also use the windows explorer, find the file you
want to open, then right click, open with (then select)
but this permanently changes the program association.
If the file is in .123 file format rather than any of the .WK?
formats, there's no way to open it in Excel. You'll need to convert
the file in a recent version of 123, or Quattro Pro from version 10
on, or using DataViz's ConversionPlus. There is *NO* *FREE* software
of any sort that works with .123 files. Microsoft provides no support
whatsoever for the .123 file format.