How to add a thumbnail to EB5 composer template?

Hello,

I have created a few new templates for my users when writing a new blog post. Unfortunately, I didn't found how to add a thumbnail to them. Right now when the choose a template appears, it only show some blank page with a title (as seen in the screenshot).

How can I add images to them?

Also, I think there is an issue with Templates and Blocks when updating EB5.
I realize that every time I update EB5, the default templates I unpublished are re-published. Same thing is happening with Blocks. I have disabled many of them but with every update, they are re-published automatically...