Domain Scan - Workstations already exist so no data collecte

I have manually added 75 workstations along with 5 assets attached to each of those workstations.

When I run a domain scan it only brings in new workstations and their details, ie the hardware/software info etc...

When I do a manual scan of the existing workstations it succeeds but does not pull any of the hardware/software info, but If I delete the workstation it grabs all the info about the machine.... This is fine but if I delete all the workstations I loose all my assets I have attached to the workstations, along with their assigned owners.

Anyway to set it up so if the machine allready exists it just updates the information into the database.

Any help would be appreciated.

Cheers