Read more button on main blog page

I am trying to shorten the posts that appear on my main blog page by adding a “Read more” button after a certain amount of words for each post that I create and then gets added to my main blog page. However I am having trouble getting this to work with the bento theme that I believe that I am using. When I go to my main blog page that I have linked here it says this “This page is setup as a “Blog Page” from WordPress Reading Settings. Thrive Architect cannot be loaded in such instances.” Therefore I can only make changes I assume with the editor that I am using right? Can some help guide me to show me where I might add some shortcode etc to achieve this? Thanks

The page I need help with: [log in to see the link]