You can create MileSplit Exports from Reports that have MileSplit Report Sections added to them. So, if you need to generate a MileSplit Export, first you need to create a Report that includes MileSplit Report Sections for each Event you have in your Race, then export that Report using the new MIleSplit Export Option.

It’s important to not change the order of the Report Sections that are generated for each Scored Event when you add them to the Report. They must be grouped together by Scored Event in order to meet MileSplit’s required formatting.

First create a report that has Milesplit sections for each and every Scored Event you are scoring that day.
Ensure that you keep each Scored Events sections together. If you move them around, make sure that the Overall List is above the Team Summary section for each Scored Event.
Once the Report is built, go to Export > MileSplit to generate the file.
Add a course name, and export to CSV. The resulting file is in the format that MileSplit requires.