Hi @MFKouk,
WorkBench is best for uploading new records to the database. Although the Catalog Number field can be used to associate new records with existing Collection Objects in the WorkBench, this does not work for all relationships.
For a to-one dependent relationship like Collection Object Attribute has with the Collection Object, we recommend using Batch Edit to add attribute records to Collection Objects.
Batch Editing Documentation:
Please let us know of any further questions you might have!