Exchange Powershell: Update User Calendar Permissions

Open Powershell and run as Admin and then enter the following commands
Install-Module ExchangeOnlineManagement
Import-Module ExchangeOnlineManagement
Connect-ExchangeOnline -UserPrincipalName user@minnesota-title.com -ShowProgress $true
Get-MailboxFolderPermission user:\calendar
Choose the permission level needed:

Owner — gives full control of the mailbox folder: read, create, modify, and delete all items and folders. Also, this role allows to manage item’s permissions;

PublishingEditor — read, create, modify, and delete items/subfolders (all permissions, except the right to change permissions);

Editor — read, create, modify, and delete items (can’t create subfolders);

PublishingAuthor — create, read all items/subfolders. You can modify and delete only items you create;

Author — create and read items; edit and delete own items;

NonEditingAuthor – full read access, and create items. You can delete only your own items;

Reviewer — read folder items only;

Contributor — create items and folders (can’t read items);

AvailabilityOnly — read Free/Busy info from the calendar;

LimitedDetails — will show the time, subject, and location, but no other information;

None — no permissions to access folder and files.
In order to grant user2 the permissions to view and edit user1 calendar items, run the following command:
Add-MailboxFolderPermission -Identity user1@minnesota-title.com:\calendar -user user2@minnesota-title.com -AccessRights Editor
Disconnect-ExchangeOnline

Be sure to disconnect from the Exchange session or else it will stay active indefinitely.

NOTE: If you need to change the permission level up or down you must remove the existing permissions and then add the new permission level. Use the following command:
Remove-MailboxFolderPermission -Identity user1@minnesota-title.com:\calendar -user user2@minnesota-title.com