nopCommerce Comments on reviews plugin will allow the user to write comments on product reviews.
The user will also show the other users comments on each review.
Admin user will able to show the list of the comments.
If an admin wants to change the comments then admin will able to edit the comments text and it will change for all user.
It is easy to install and configure the plugin and you are good to go ahead to use it in your NopCom Site.
It is NopCommerce 3.9 and 4.0 supported standalone plugin.