Editing or adding to Shop Search Words needs to be done to one product at a time on a product by product basis.
If you have a large number of products you wish to update you may want to consider doing this going forward or go through your back catalogue incrementally.

Your catalogue will continue to update as you add more information.
You customers will still benefit from predictive search even if the Shop Search Words are not included with products seeing as search also uses all keywords and phrases taken from:
Product name
SEO keywords
Product Code
Product variation options
Collection names

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