How do you sync from one calendar account to another?

I am trying to migrate from a broken calendar account (no remote sync access, but the phone has all the data cached locally) to a self-hosted CalDAV calendar (connected to by DAVx ). Both calendar accounts are in DAVx, and both are visible in calendar apps. Question: How do you export an existing calendar to another calendar on the device? I have both the "Google Calendar" app and the default Calendar app that comes with LineageOS, but neither appear to support export/import---or at least I cannot find the option. There are _lots_ of calendar events, so we need to do it in bulk. With contacts, it is simple: you can export a .vcs to a file and import the .vcs to another contact account with the "Contacts" app. But with I can't figure out how to do the same thing with a calendar account. Ideas?