If you want to export specific columns to CSV file in Calendar Plus web Part, please follow the steps below;

1. Navigate to Menu Bar "Configure Control" and click on the ellipsis near the "ExportNoLable" option within the "Top Actions" section.

2. Paste the code provided in the link below to the "Write your own JavaScript code for this function:" field:

 

component.exportCSV(root, component, item, [
  { InternalName: 'Title', Title: 'Subject' },
  { InternalName: 'Id', Title: 'Id' },
  { InternalName: 'dvp_EventDate', Title: 'Start Date' },
  { InternalName: 'dvp_EndDate', Title: 'End Date' },
  { InternalName: 'attendees', Title: 'attendees' },
  { InternalName: 'organizer', Title: 'organizer' }
]);

3. The code above specifies the columns to be exported with their corresponding internal names and titles. You can customize the list of columns by adding or removing entries in the array.
Here is the list of all the columns available in Calendar Plus when connected to your Outlook Calendar using Graph API:

dvp_FileType	dvp_ViewFormUrl	dvp_DataSourceName	dvp_DataSourceId
Id	Title	start	end
subject	body	bodyPreview	type
location	attendees	organizer	categories
isAllDay	importance	recurrence	dvp_format
dvp_Subject	dvp_Location	dvp_Description	dvp_Categories
dvp_EventDate	dvp_EndDate	dvp_IsAllDayEvent	dvp_IsRecurrence
dvp_Attendees	selected	highlight	unseen

       '@odata.etag'

4. After following these steps, you will see additional columns have been added when you export to CSV format.