To remove item (meeting) from meeting\conference room hosted on Exchange when users left the company

In Exchange management shell:

Get-MailboxFolderStatistics -Identity RoomName -FolderScope calendar
Look at the FolderPath it could be different
FolderPath                        : /Kalendarz
FolderPath                        : /Calendar

Add-MailboxFolderPermission -Identity RoomName:\Kalendarz -User -AccessRigh
ts owner

Then You can remove any meetings from RoomName meeting room using Outlook