How do I transfer the configuration on our existing SBC to the new SBC?

You can do a database backup from the existing SBC, download it, and upload it to the new SBC, validate and recover it:

https://docs.telcobridges.com/tbwiki/Toolpack:Database_Backup_C

https://docs.telcobridges.com/tbwiki/Toolpack:Restoring_a_Database_Backup_C