I'm not exactly sure what you are asking, but you can create a review submission form to collect reviews. You can include links to other review sites so they can go leave a review there if they want. However, the plugin can not submit a review to Google for the customer. Google or any of the other sites require the customer leave the review on their site.

I would need to log in to your site to investigate. You can send temp admin credentials to landjllc@gmail.com if you want me to take a look.

It checks the name and timestamp of the current reviews in the database and compares them with the import. If a duplicate is found it skips it. So, they add unless already in there. They do not overwrite.