As you probably know each product can have own unique "related products pro". To manage lists of "related products" just go to product edit page and go to "modules" section. You can manage there list of "related products" - create new, edit existing etc. You can create there lists of "related products individually for each item or create "global" blocks that will appear on many product pages.
On product edit page, on module section you can manage list of created "related products" instances you created with the module. You can create here also new "related products" instances for item that you currently edit and even for other products (module has features to decide on what product pages you want to display created "related products" instances)