Delete Calendar Entries in

Outlook version
Outlook 2013 32 bit
Email Account (as MS Exchange)
I want to delete all entries in my Office365 OWA Calendar.
Reason for deleting is that my Offline Calendar is perfectly all right and has some 1233 entries whereas Online Calendar in Office OWA has some 2,000 entries. This creates reminder at odd times.
I want to delete all entries in Office OWA account which will delete in my Microsoft Outlook Calendar and all devices. After successful delete, I will import the Calendar PST file which is perfectly all right.
If I delete from Microsoft Outlook by switching to list view, All Online records will NOT be deleted and hence I have to compulsory delete all entries from OWA.
Outlook version
Outlook 2016 32 bit
Email Account
Office 365 Exchange
the folders should be identical - and i dont think there is an easy way to delete from owa, not like there is in outlook.

if you delete all from outlook, wait for the sync and then right click on the folder and choose properties, clear offline, do any more sync down?
Outlook version
Outlook 2013 32 bit
Email Account (as MS Exchange)
Thanks for your reply.
Clearing Offline Calendar entries will not clear orphan entries in OWA which is creating havoc.
My Contacts too were messed up and I deleted all contacts from OWA which deleted offline contacts. I imported contacts in Microsoft Outlook from a saved PST file in which I had exported only Contacts and then they Synced with OWA. I want to do similar exercise for Calendar entries.

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