I don’t know what your comments.php looks like, so I cannot tell how to adapt your current code, but I can generally tell you how to approach this.
Normally, WP will assume that you want the latest comments of the current post. If you want something else, you start with the condition under which you want your second set of comments to show and add this to comments.php: if (my_condition) { show second comments set; }
Now, you have to tell WP which set of comments to use. You need to set $args which are available in the get_comments function. There are too many options to describe here.
Once you have retrieved comments with $comments=get_comments($args); you can feed them into the display function wp_list_comments($args,$comments). The $args to this function determine how the comments are displayed. You can have them shown completely different from you other comments set.