Thank you so much Chrisroll!. that worked!
https://wordpress.org/plugins/relevanssi/#description
Relevanssi plugin zip file uploaded , plugin activated
From within plugins:
Relevannssi>Settings>Indexing> post types (I ticked “page” and “product”) taxonomies I ticked “Category” and “product_tag” Expand shortcode untagged > Save these options
Indexing > build the index (took < 1 min) , went to search, searched for Knautia – it worked!