Product social share image automatically shows third image. How can I change it to the first image?

[vikasnair]

My store is www.redoak.in. When I share a product link URL on Whatsapp, it shows the social share image of the product along with the URL, which is great. But for some reason it picks the third image out of all the product images. I want it to show the first image. How can I fix this issue?