Move the remaining arbitration mailboxes
After you've verified that the migration mailbox move has completed successfully, you can move the rest of your existing arbitration mailboxes to Exchange 2019.
In the EAC, go to Recipients > Migration.
Click New, and then click Move to a different database.
On the New local mailbox move page, click Select the users that you want to move, and then click Add.
On the Select Mailbox page, add the following mailboxes:
DiscoverySearchMailbox{D919BA05-46A6-415f-80AD-7E09334BB852}
FederatedEmail.4c1f4d8b-8179-4148-93bf-00a95fa1e042
SystemMailbox{1f05a927-XXXX-XXXX-XXXX-XXXXXXXXXXXX} (for example, SystemMailbox{1f05a927-7bd0-47e5-9b6a-0b5ec3f44403}; most of the mailbox name is unique to your organization)
SystemMailbox{bb558c35-97f1-4cb9-8ff7-d53741dc928c}
SystemMailbox{e0dc1c29-89c3-4034-b678-e6c29d823ed9}
When you're finished, click OK,and then click Next.
On the Move configuration page, enter the name of the migration batch, and then click Browse next to the Target database box.
On the Select Mailbox Database page, add the target mailbox database. Be sure to select an Exchange 2019 database (Version 15.2), click OK, and then click Next.
On the Start the batch page, select the options to automatically start and complete the migration request, and then click New.