How to change page template for Posts Page in Illdy

I really like the Illdly theme, but am have a few issues getting some items the way I want them.

At the moment, the key thing I want to do is use a different page template for the Posts Page (and ideally each of the Posts themselves).

If I go into any normal page, in the Page Attributes section, I can change the Template from Default Template to Left Sidebar or No Sidebar. The Left Sidebar is currently setup with Categories and Archives. I want this to show up when users go to my Posts Page, but when I open the Posts Page, it does not offer the Templates dropdown in Page Attributes like other pages. Nor can I see anything in the customizer to make this change. Please advise.

Also, if I want all my posts to display using the same template (i.e. left Sidebar), how would I do that?