It’s an error within your theme microdata. The best thing to do is to contact your theme provider and have them resolve it. Alternatively, you can install an app to provide structured data for you.
Your theme is using incomplete microdata instead of JSON-LD for the structured data which makes it even harder to fix.
Since Shopify doesn’t support their older themes anymore, you should consider setting up a new theme (which should happen anyway) and/or installing a structured data app like JSON-LD for SEO. We don’t remove the old microdata, rather we create a whole new set of data that Google can use. Google will ignore data with an error. If you want to remove your microdata, you can use this guide. But you’ll want to replace it with a correct structured data set to qualify for search enhancements with Google and Bing.