To install IntelliTicks on a Shopify website, just follow these basic steps
Log into the Administrator Dashboard for your Shopify site.
Search for "Themes" from the top search bar, you will see an option Themes as shown in red rectangle. Click on that.
In the Themes page, you will see the current theme live on your website. In the theme preview you will see an option "Customize" as shown below. Click on that.
This will take you to the theme editor page.
In the page, on the left-side menu, you will see many options. Scroll to the bottom of the left-side menu to reach the drop-down button Theme Actions
Clicking on Theme actions, will show three option, click on Edit Code
In the Code Editor panel, you will see a list of files being used with your themes. Under the Layout folder, you will see a file theme.liquid. Click and open that file for editing.
In the theme.liquid file you will see the <head> section of HTML. Just after the meta tags, insert IntelliTicks script from IntelliTicks Admin console
To find IntelliTicks script follow steps in this link
After putting the code, save the file & you are done.