This is the error Google get when the URLs are missing but the server doesn’t send 404 response. Under each tab a list of all the URLs for which Google is getting the respective error. Under both the tabs, you will find the Soft 404 and Not Found errors. Now, there are two main tabs under URL Errors, Desktop and Smartphone. On the left hand sidebar click Crawl and then Crawl Errors. If you have the search console set up already, login and go to the dashboard.
The Search Console is the most important tool you need for monitoring the SEO health of your store.
If you haven’t added your store yet then first submit your Shopify store and the sitemap in Google. The best place to find those 404 error is in the Search Console of your Google Webmaster Tools account for your Shopify store. Because those errors directly hurt your SEO.