This article will help you know how to add/edit/remove a product metafields in Shopify with the Metafields Guru app. IF you don't know what metafields is, please refer to this article https://www.shopify.com/partners/blog/110057030-using-metafields-in-your-shopify-theme.
From your Shopify admin, go to Apps.
Click the Visit the Shopify App Store button to go to the Shopify App Store.
Search the app with terms: "Metafields Guru".
Click the app like the below image, then click the Add app button to go to the Installation page, then click the Install app button to install it.
From your Shopify admin, go to Apps > Metafields guru.
Click the Products & Variants row.
Find and click the product you want to add product metafields.
In each metafield, you can edit the namespace, key, type, and value. Click the Create metafield if you want to create a new one. Then click the Save button to save your changes.