you already share it with will appear in the Sharing Permissions window. Click the Delete button (trash can icon) next to it to stop sharing. How to share a calendar in Outlook from your phone ...

Open Outlook and click "Calendar" in the menu at the bottom-left ... You can also change the default permission level by selecting "Choose your permissions" — you can switch it to "Can view ...

That is why Outlook often tells you that you don’t have permission to read or write. In that case, you need to download the MFCMAPI tool, select the appropriate Microsoft Exchange Message Store ...