How to manually update a record during the process of a service catalog item?

I am looking for a way to have a person manually update a record during the process section of a service request.

When we I add the update record item in the process section, it doesn't let me add the item unless I choose a value for the field right then.

How can we add fields in the process section that need to be manually selected by the person assigned to the service?

It looks like this should be possible in the process field, but it seems to be missing Service catalog: