Depends on how exactly you plan to use it. For programmatic access, EWS or Graph API based solution would do. If you need to access each calendar via Outlook, add folder-level permissions on each calendar for said account. Something like this:
$calendars = Get-Mailbox -RecipientTypeDetails UserMailbox | Get-MailboxFolderStatistics | ? {$_.FolderType -eq "Calendar"} | select @{n="Identity"; e={$_.Identity.Replace("\",":\")}}
$calendars | % {Add-MailboxFolderPermission -Identity $_.Identity -User Email address removed -AccessRights LimitedDetails}
Adjust the permissions as needed.
