WooCommerce Blocks

ok, the problem is that I have over 600 product and some product has over 100 variations. For those colour variations I use colour codes so visuality is important on the variations.
The products made from the same crystals so I use the same variations on different product.
On wordpress customers check the products parent img. So they know how the product look. Then choose the variation.
I would need a general option in woocommerece for facebook to use the parent img first when show the products.
Now if I use the normal setting then the facebook use random variations to show as first img.. right now it looks like all products are the same like this..
If I would change the approx 3700 variations manually to use the parent img than customers would not be able to see the differences between the variations..
So I would need an option to pick in the general setting somewhere..
so facebook show the woocommerece parent img as product img, and variations as variation img.
pls someone give me a solution.. without telling me an other site where I should ask for solution..
simple products are working good.
all solution I heard is good with a simple product.

Foldal

https://www.dropbox.com/sh/q98txagms72qkup/AABPxtugS-QU23Bx4_coTkL6a?dl=0