Hi @Alik ,
- If the employee who left the company still has an active Office 365 account, you can ask an Office 365 admin to grant full access and send as permission to that account. Then, the admin can configure the account in Outlook and cancel the meeting from the employee’s calendar. please refer to this article: Cancel a meeting.
- If the employee’s Office 365 account has been deleted, but it is within 30 days of deletion, you can temporarily restore the account and assign a license to it. Then, you can convert it to a shared mailbox and remove the license. After that you can add the Full access and Send As permission of the shared mailbox to the admin account based on same methods I mentioned above and access the shared mailbox to cancel the meeting.
- If the employee’s Office 365 account has been deleted for more than 30 days, or you don’t want to restore it, you can use a PowerShell command to search and delete the meeting from all recipients’ mailboxes. This similar thread for your reference: How to Remove Calender Invite from Deleted User for all Recipients?
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