Your customer is using the baseline Create Incident Catalog Item and would like to add a few additional input fields. How should you update the catalog item?
You can create or edit a catalog item (catalog item or record producer) using a visual and guided experience along with specified restrictions. The catalog builder experience enables you to delegate the creation and maintenance of the catalog.
https://www.servicenow.com/docs/bundle/xanadu-servicenow-platform/page/product/service-catalog-management/concept/catalog-builder.html