Asset Field _ 2 previews only
In this example I'm seeing 2 fields that are part of my Asset object field. I'm looking for a way to increase the fields I can see in the preview to 3 fields. Any suggestion?
You can modify the fields that you see in the search. But you cannot add more than 2 fields (secondary field) in the results. The secondary field is configured in the Search Layout for the object and is displayed on lookup fields.
From documentation for Lookup Search in Lightning Experience
What Determines the Secondary Field Under the Record Name?
When available, there's a secondary field displayed under the primary record name in lookups that provides more contextual information. For example, the location San Francisco appears under the company Acme, Inc. to help you distinguish similar record names and pick the right record. Your admin customizes secondary fields when setting which record fields display and in which order.
As how to configure the secondary field, take a look at Configure Lookup Search Results in Lightning Experience.
Lightning Experience makes it easy to set up lookup search result layouts. Verify that the search layout used for an object’s global search results are also useful for lookup search results. Also make sure that the second field chosen in the layout is a field that could be used to distinguish between similarly named records.