export/import entries in the One calendar app on my Android phone

I suffered a disk failure on my Synology NAS and I had to re-install DSM and all applications on it. From the past I know that starting synchronisation between the One Calendar app on my Android phone and Calendar Station on the NAS results in loss of all existing entries in de One Calendar app on my phone (which seems logical as a newly installed Calendar Station has no entries).

Is there a way I can export the calendar entries in the One Calendar app on my Android phone, so I can import them after starting synchronisation with Calendar Station? Or a method to start synchronisation with One Calendar Station while retaining the current entries in the One Calendar app?