Adding JS library BEFORE head area

I am so struggling with this.
There are area for adding in HEAD and Body, or for SEO
but There is NO are that I can import JS library BEFORE HEAD.
Below is the description that I recieved from the site that provide JS library.

How to Add the Library

Add this script to the site wide custom code before HEAD area of your site.

Hi Shinhee, in Webflow the custom code area for HEAD-inserted custom code is referred to as the “before </head>” or “before head” area. There is only one such area. You’re in the right place.

What are the code of js or css you want to add before head area? Please share ?
Why you want to add js or css code before head area?
You can add javascript or css code in HEAD and BODY area.
If you want to add code BEFORE HEAD then it will reduce speed of your website.

async and defer scripts load faster in the head.