@ebetech : The no-featured-image images is used as a placeholder and you are supposed to upload featured images on every post as this theme heavily relies on featured images. If you would like to replace the default images with your own images, you will need to copy every function that displays no featured images and replace get_template_directory_uri()
with get_stylesheet_directory_uri()
in each function. If you do not have knowledge with child theme customization, i suggest you to hire a customizer
Let me know if you have any more issues.
Regards,
Tikaram