Add text to the top of a blog page

My client has a WordPress website. One page is set up as his blog. I would like to be able to add a sentence at the top of the page, above the page title and the “recent posts” widget, which tells newbies how to click the title and leave a comment to posts. I am not fluent in hand-coding but can do it with explicit directions. Can anyone tell me how this is done?

The site is: https://www.crimesagainstpeace.org

Thank you!