How can I add the ability to export to a csv file? Right now the only export option on the actions menu is to a Microsoft Excel file.
What version of Civi are you using?
Under Events > Reports > Participant List, Mine shows "Export CSV" as an Action Option
Under Search > Find Participants, it just says "Export List", But when I export it I get a CSV file.
But even if you get a .xls or other Excel file you can always save it as a .csv in Excel. If you do not have Excel, then run it through an online file converter. You can even open the Excel file in Google Sheets and then download it as a csv to convert it.