How do I map data to user fields to be available in WMS label printing?

I am trying to map a few fields to the item label in WMS.

Following the instructions here: NetSuite Applications Suite - Creating Custom Print Templates and Files (oracle.com) it mentions mapping user fields.

—The standard source records may not include the data you want to use for your label or document. Note the following options when setting up additional data:

• You can use the ten additional fields, named User Field, included in the standard source records.

For example, the source record for the standard WMS item labels is the WMS Auto Printing Rule Evaluation Data record. It supplies the data for the item name and item description that appears on standard item labels. This source record also contains other preconfigured item and transaction data, such as the item quantity and transaction number. If you choose this source record for your template, you can use any of these available data.