How to Verify your Domain in Google Merchant Center?
2. To verify the domain go to "I have access to my server" box.
3. Select the method "Add an HTML Tag to my homepage".
4. You need to then edit your theme as you will have to place the meta tag that Google provides you in your theme.liquid file.
5. When Google redirects you back after verifying your domain you will see a link to Claim this URL, click on it and your store will be ready for the next step