I don't know what QRadar version you are on, but this answer is version dependent.
In QRadar 7.3.3 (and earlier), there are two options.
- You can use the API in QRadar to import assets /asset_model/assets/{asset_id}.
- There is a utility called asset_updater.py that you might also be able to use to import values from a CSV file. https://github.com/ibm-security-intelligence/data-import/tree/master/assets
In QRadar 7.4.x, there is only the API option to update assets. I've heard that the utility does not work with QRadar 7.4.x. So, the API is going to be your best bet. You will need to know the asset IDs, then you can post the values in through the API. 
#QRadar#Support#SupportMigration