How to change from one to two columns?

Unfortunately, the theme alone does not offer this view. But you can use the Gutenberg editor for it, as follows:

Create a new page where you want to list your posts in the future. In the Gutenberg editor, select the Query Loop block. In this block you can configure that you want to display the posts in 2 columns.
If you have used a blog page so far, you should deactivate it and change all links to the 2 column view to the newly created page.