Admin - need to edit the URL of the header, don't have access

I need to change the link to one of the clickable frames in the header of my forum.
I’m an Admin.
After searching the internet, found this guide:

However, I don’t seem to have an access to CSS/HTML. this is what I see:

Am I missing something here? I’m supposed to have the highest permissions.

You go to Themes > Components:

If you want to make changes to an existing header, it’s either build with a component already or with custom theme code. So you’d need to make adjustments through that component or on the theme code.

If you want to add a new component (as on your guide), you select “Install” and then “+ Create New” from the modal.