Step 1: Upgrade
Strikingly allows you to insert custom code in header only in paid version.
Step 2: Insert code
Your code is in Smartlook > Account > Sites > Tracking code.
In case you have Strikingly paid version insert our code as you see in screenshot below.
Step 3: Refresh site
Now go to your site homepage and refresh browser.
To see visitors on your website log in to Smartlook.