How to modify thumbnail image on Facebook share

We used an existing template from an online pet bakery to create a bakery order form for my wife's home (human) bakery business. The form works and looks great, but when we try to share it on Facebook, it auto-generates images from the original pet bakery form. How do we modify the associated thumbnails so that when we share her link, people don't think they're ordering dog treats, but human treats?!

I've cloned your JotForm to my account and tried sharing the cloned form link which worked without any issue.

However, I see that the issue presents with your JotForm. I'm checking on it and get back to you as soon as I find some information for you. Could you try cloning the JotForm to your account again and see if the cloned form is having the same issue?

Thank you for your patience. 

Yes, the cloned form works fine. I guess I just replace the links we've shared elsewhere with the link to the new cloned form?

If you are using the cloned form, then yes, replace links to the original with links to the new clone.