Navigation links missing on my customised theme

Hi,

I started ages ago with someone elses theme and over the years have hacked it into a form that’s nowhere near its original form, however I’ve also broken something and the byzantine structure of wordpress means I can’t find out where.

Basically it’s customised so that in general we use pages as if it was a standard html website but with a blog section tagged on. On the blog list though, we’ve lost the navigation link that allows you to look at old posts. Where should I look for this to restore it?

the problem is at
https://www.newoperahero.com/wordpress/category/blogs/

thanks for any help you an give me. I’ve been staring at this for days!