Sales Channelsfrom the left hand side menu.
Themes, and you'll see your active theme. There is a button with 3 dots in it ("..."). Click on this and you'll see a dropdown menu.
Edit HTML/CSS. This will open the theme editor.
Layoutson the left hand side menu of the editor, you'll see a file called
theme.liquid. Click on this to load it.
Album Embed Optionsand paste into your this file above the closing