If you mean adding these to the keyword search please mark attributes as Indexable. If you mean displaying the attribute fields in the search/filter forms you can try marking them as Filterable/Searchable.
This depends on the attribute type, for example text/number attributes (non-selectable) are stored as meta fields in wp_postmeta table with “hp_” prefix in meta keys. Selectable attributes are stored as terms in wp_terms table, with “hp_” prefix in taxonomies. Hope this helps.