How can I change the thumbnail when the link is sent?

May we know via which platform are you sharing the link?

You need to add a Header with an image or an Image field in your form first. The image will be used as the thumbnail image when you post the link of the form on social media.

Looking forward to your response.

Thanks.

Messenger/ Facebook mostly
Thanks
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So have you added the image in the Header or the Image field? Are you able to see the custom image in the thumbnail?

Looking forward to your response.

Thanks.