If you're unable to find the "csv-ms-dos" option in Excel, you can try the following alternative approach to save your CSV file in a compatible format for VOSviewer,
Open your CSV file in Excel.
Click on "File" or the Office button (depending on your Excel version).
Select "Save As."
Choose a location to save your file.
In the "Save as type" or "Save as format" dropdown menu, select "CSV (Comma delimited) (*.csv)."
Click the "Save" button.
This should save your CSV file in a standard CSV format that should be compatible with VOSviewer. You don't necessarily need to convert it to "csv-ms-dos." After saving it in the standard CSV format, try importing this file into VOSviewer to see if it works.