To implement Yieldify manually (without the help of a CSM or a tag manager), you'll need to copy the tag from the Settings page and place it just before the </head> tag on every single site page.

We'd recommend against integrating our technology this way and would push the use of a tag manager or similar - this is because tag managers universally apply a tag, making it much quicker to integrate. Aside from this, changing code on your site or adding new pages/products mean integration is an ongoing task.