In this Article, We will see out to restore mailbox in Exchange Online.
In my test Office 365 Tenant, I have three Users in which i am deleting one user to show you how to restore the mailbox to the another mailbox
You can see the mailbox in the deleted Mailboxes. Note: Once you delete mailbox in Office 365, it will be there in deleted mailboxes for 30 days post that Mailbox will be permanently removed from the tenant.
Get-Mailbox -Identity Arun.r -SoftDeletedMailbox | fl *guid*
New-MailboxRestoreRequest -SourceMailbox 6610f39b-f473-4fa7-8fa5-5ccad5a719fa -TargetMailbox eswaran.g@Windowstechpro.onmicrosoft.com -TargetRootFolder restore
Here, SourceMailbox  Guid is softdeleted mailbox and the target mailbox is restored mailbox and it will be stored under TargetRootFolder restore