Hello, @munji
For this, you should use lifecycles (create/update).
When you create/update a product in strapi, you should make a request to a custom service which will make a POST/PUT request to Shopify with the data of the product. When creating a product, shopify will return an unique ID, you should then store this id inside strapi. Then for updates you should use the shopify’s id when making the request to update a product.