How can I edit the “blog / archive” page for posts?

Something is wrong in the code of my theme Catch Sketch "free" It will not allow me to add a featured image or content description of the "blog" page before a post which will be shown on the "blog" page. I am no longer able to have a specific feature image used just for the "blog" page I created or have text paragraph block which describes the content of the posts that follow. Now I can not do either even though I created the initial blog page first the way I want and then go to customize tab and homepage setting and select this as the page for "posts" to be directed to or housed under. It ignores or removes the contents of the "blog" page. Here is my page in question: https://www.axumcreative.com/street-portraits-la-blog/ 1. I would like to change the "archive" text and grey area to a featured image (currently it wont update). 2. I would like to place a paragraph block of text between the featured image and page title "Blog" or right after to describe the content of the page. 3. I would like to be able to change the word "Blog" to something else like "Articles" I have tried creating a "blog 2" page and testing to see if it was an error with the first "blog" page and the same thing happened. I do not know what to do. Please advise.