Tell us what you are trying to do? I have a custom field image that I would like to set as the Featured Image upon submitting a form.
Is there any documentation that you are following? I've looked around but none of the other support tickets show how to do this... I'm thinking some custom function upon creation of the CPT.
Is there a similar example that we can see?
What is the link to your site?
You'll need a custom code if you want the Featured Image to be saving the Image Field value.
If you just want to display the Image Field in place of the featured image on the front end you could use Toolset's ShortCodes to display the Image field in a Content Template and apply this over the Posts Content (but your theme would need to not display the featured image)
If you want the value to be saved in the database you need custom code.
This can be applied on a Toolset Form with the cred_save_data() or on the backend when saving the Post on the WordPress native save_post()
More information about those hooks can be found here:
https://codex.wordpress.org/Plugin_API/Action_Reference/save_post
https://toolset.com/documentation/programmer-reference/cred-api/
To update the feature image in the database you will need to address the Post Thumbnail for example with https://codex.wordpress.org/Function_Reference/set_post_thumbnail set_post_thumbnailI() used within either of above-elaborated hooks.