PowerShell might be a better choice since SharePoint Designer 2013 workflow needs a manual trigger or to be built on a specific object.
If the personal calendar is saved in a SharePoint list, here is a sample script you can use to add new events:
$SiteURL = "<SiteURL>"
$CalendarName = "Calendar"
#Connect to PnP Online
Check your Web Part Page for additional hidden calendars.
Choose Edit Properties from the Page tab of the ribbon. From there, select "Open Web Part Page in maintenance view." Check and delete any extra calendars you don't want, or, to be safe, delete all of them and re-add the calendar you want.