When you activate plugin, it adds a menu option under Settings > Header and Footer. That’s where you’ll find “Scripts in the header” text box.
It’s possible to do without plugin, but that requires changes to your theme. If you make changes to theme files, you will no longer be able to update your theme. If the theme is already customized and you don’t update it, then it shouldn’t be a problem.
You can paste the code I sent above inside your header.php. Make sure you paste it before </head>
tag.
See this screenshot:
https://share.projectarmy.net/ce1fc3a4-2e0f-4e10-998f-3ae3d72a43ea
Please note, if you’re using File Editor to edit this file (under Appearance > File Editor) be careful pasting this code. Smallest error can cause an error and lock you out. Follow instructions above, or use the plugin.