How can I link the form to the event picture click on the FB Page?

If I understand correctly, you want to link your form to an image in facebook so that when it is clicked, the user will be redirected to the form? Unfortunately that is not possible to achieve. You can only add the form to your facebook page by following this guide: Adding a Form to Your Facebook Page, or by sharing the direct url to the form as a post.

Please let us know if you need further assistance.
Thank you.