Not sure if you are using the free or paid version of their theme, but I added the free version to one of my sites and here’s how to disable that author box at the bottom of the blog posts.

Go to the theme settings: Appearance > Themes > then click Customize on the Polestar theme. Click Blog, then scroll down those settings and make sure ‘Post Author Box’ is unchecked.

Hope that helps, but if you still have questions just let me know.

Take care,
Andrew