After more reading, it's not in the reviews the attribute hreview-aggregate must be, but on a "top" div containing all the product information.
First try to add to title, but result is bad (stars appears, but google complain about informations missing, but they where there)
After I add it in content-single-product simply by adding a upper level div with just div class="hreview-aggregate" and closing it at the end of product page.
This is working well, google see everything in hreview (number of votes, average and notes, price, description ...) and just give an advice as it's the attribute "count" present and not vote, it must have the attribute "reviews" and it's not the case
This attribute must have a place in review.php this time, but will see later