Both .wks and .123 files are somewhat obsolete spreadsheet files by todays standard and not many spreadsheet programs support them. And even if they can import the data, they usually do not offer means to save in these old formats.
So unless you find the original Lotus spreadsheet program on some abandonware website, achieving wks to 123 conversion may be a little tricky. You can always try OpenOffice.org programs, but ancient formats are usually abandoned in latest versions and only old versions might have supported them.