Seeding a database copy can be performed from the Exchange Management Console (EMC) or the Exchange Management Shell (EMS). The database will always seed from the active database when you perform the operation from the EMC. If you want to select a different source you need to use EMS.
Open and elevated EMS prompt and run the following three cmdlets:
Add-MailboxDatabaseCopy -Identity DB01 -MailboxServer EXMB03 -SeedingPostponed
Suspend-MailboxDatabaseCopy -Identity DB01\EXMB03 -SuspendComment "Seed DB01 from EXMB02" -Confirm:$False
Update-MailboxDatabaseCopy -Identity DB01\EXMB03 -SourceServer EXMB02 -DeleteExistingFiles
The first command adds a new mailbox database copy of database DB01 on mailbox server EXMB03, but does not start the seeding operation. Once this operation completes you will see the DB01 database copy on EXMB03 will be in a "Failed and Suspended" state.
The second command suspends the mailbox database copy and creates a suspend comment. This step is not necessary, but it's helpful to create a comment so other administrators don't try to "fix" the failed and suspended database copy.
The third command seeds the mailbox database copy on EXMB03 from the source server EXMB02. It also deletes any existing DB01 database or log files on the target prior to seeding. Once this operation begins the database copy state will change to "Seeding" until the seeding operation is complete, at which point it will change to "Healthy".