From your Shopify admin, go to Online Store > Themes.
Find the theme that you want to edit and click Customize.
In the left-hand toolbar, click Theme settings.
Pick or upload your image to display it as a favicon. Your image should be a square.
Display the number of items in the cart on the browser bar.
Enable: show/hide the badge.
Position: pick a position to display the badge.
Background color: pick a color for the badge's background.
Text color: pick a color for the text.