How to populate fields in the 'General Information' section of an item within a purchasing catalog

We would like to understand how to edit the fields displayed in the General Information section of an item within a purchasing catalog.

Currently, when we access one of our catalogs in the Purchasing Requisitions work area, we can view the items listed. Clicking on an item opens the 'Product Details' page, which shows the item's description and price under the Product Details section. However, there is also a General Information section that provides additional descriptive fields.

We are specifically looking to populate fields such as Supplier, Supplier Item, and Comments, but we haven't been able to determine where to do this. I've explored the "Manage Items" function in Product Information Management but haven't found a way to populate these fields.