In Exchange Online, this example uses the Get-Mailbox cmdlet to find the ExchangeGUID value of the mailbox, which is required to restore the mailbox contents. Target mailbox could be some empty shared mailbox.
Get-Mailbox -SoftDeletedMailbox "Email Address" | Format-List ExchangeGUID
New-MailboxRestoreRequest -SourceMailbox "ExchangeGUID" -TargetMailbox "Email Address" -AllowLegacyDNMismatch
Show the progress of mailbox request:
Get-MailboxRestoreRequest