The auto-ads code uses the single code snippet to generate ads everywhere on your WordPress website. This means you need to add the code to all the pages where you want to display the ad.
One way to do this is by adding the code in your WordPress theme’s header.php file. However, the disadvantage of this method is that your ad code will disappear if you update or change your theme.
The best way to add any site-wide code to your website is by using a plugin like Insert Headers and Footers.
Upon activation, go to the Settings » Insert Headers and Footers page. From here, you need to paste your Google AdSense code in the header section.
Go to Plugin and search the Insert Headers and Footers plugin then install and active the plugin. when you activate the plugin. Go to setting and click on Insert Headers and Footers
And paste the where you want to paste and save it