Restore Mailbox from Backup and connect it to other Mailbox

hi all,

is it posible to connect a Mailbox from a Backup to other User?

example:

RDB Database has a Mailbox UserA. I will Connect it to Demo11

My try:

I disable Mailbox Demo11

New-MailboxRestoreRequest -SourceStoreMailbox "demo10" -SourceDatabase "RDB" -TargetMailbox "Demo11" -AllowLegacyDNMismatch

The operation couldn't be performed because 'Demo11' couldn't be found.
    + CategoryInfo          : NotSpecified: (:) [New-MailboxRestoreRequest], ManagementObjectNotFoundException
    + FullyQualifiedErrorId : [Server=EX2,RequestId=03aadaa1-4461-415d-beeb-a8226a48d75e,TimeStamp=28.03.2019 07:29:59] [FailureCategory=Cmdlet-ManagementObjectNotFoundExcept

Chris