The main web site has a page on this.
https://en.support.wordpress.com/enable-disable-comments/
The only catch is that with the latest WordPress, you have to go to Screen Options at the top of the screen and check the module you wish to display. In this case:
(1) Go to Pages
(2) Click on the page title
(3) Go to Screen Options, and check Discussion
(4) look at the bottom of the page and check/uncheck the discussion options
