Help making a custom function

Hello, I have been using your plugin on a client website for a couple years. The client is very picky and I had to create an extra indicator on the reviews. This new column allows me to look for verified clients. I was using this meta_key “_rating” it seems I must’ve updated to a new version of the plugin and this meta field is no longer used. I do see there is a column named “_submitted” with the rating hidden with a long json string. Is there somehow I can get the value with MySQL?
What I need is a query that looks for all reviews with my unique tag and then gets the count and average of those reviews.

Not sure if there is any way you can help me accomplish what I need to do.

Thanks,
TC