Below are the steps you need to follow in order how to turn off comments on Facebook:
You need to move to the post on the profile you want to restrict comments
On the top-right corner, tap the three-dot option.
You can select the people who can comment on your post.
To select from the options listed, you must select one of the three options: friends, profiles, pages you mention, or public.
Follow the steps above to turn off Facebook comments and prevent specific people from leaving comments on your post.