Currently, the plugin can only add the values that are in the settings plus the Aggregate and individual review markup. You can use the @id field to link the schema to other schemas on the page. So, it is possible to use another schema plugin and link the 2 together.

https://www.google.com/search?q=Schema+%40id&oq=Schema+%40id&aqs=chrome.0.69i59j69i58.319j0j7&sourceid=chrome&ie=UTF-8

Delete all your Facebook reviews. Then go check this setting. Make sure you click the "Save Settings" button after and then re-download the reviews.

Try going to the Review List and deleting all Facebook reviews.

Then go to the Get Reviews > Facebook page and click the "Get Access Code Here" button. Make sure the app is granted Facebook permissions and your Facebook page is checked in the list at the bottom. If it is, then uncheck and recheck it to refresh the auth token. 

Then go and try to download the reviews again. Make sure to leave the pop-up box open for a few minutes after it downloads.

Have you tried the Review Funnel method? See this link in the forum...

https://wpreviewslider.userecho.com/knowledge-bases/2/articles/323-google-only-downloads-5-reviews-how-to-get-all-google-reviews

There isn't a time frame. I'm currently not adding any site to the normal download methods. The Review Funnel method uses a 3rd party scraping service so I can only get reviews from the sites they support.

If you want to change them all at once you have this option in the template settings...

If you want to change them individually, then you can edit the review on the Review List page.