how can I edit the posts page?

Hiya. I have been using the inkness theme for a couple of years and really love it. My whole site it static but I recently decided to add a blog element to it (Ramblings in the menu). Unfortunately I can’t seem to edit the posts page itself to reflect the static pages (they all have a header image). Is there an easy solution to this issue? Am I missing something? Will I have to edit the code? Where exactly do I do that only for the posts page and the posts themselves.

My website is https://www.threefour.com.au

If I’m unable to change this particular aspect I’m going to have to change my theme (otherwise it looks totally inconsistent) and I’d seriously hate to do that.

thanks!