The "Sync with Algolia" trigger (which appears in the Shopify admin on the page of an individual product) updates the individual record in the Algolia index.
After making changes and saving the product, you can manually trigger "Sync with Algolia" on the product page by selecting "More actions" > "Sync with Algolia".
You can also trigger "Sync with Algolia" on multiple products, up to 50 at a time.