Currently the theme does not have feature to display the header image in the front page i.e. home page and as much as we would love to help you, we are unable to as it require higher code customization .
Our suggestion to you is to hire a professional developer for your customization, so that your theme will no be effected in any way.
The demo version has the slider section only at the front page but not the header image .
So if you meant by the slider then you can set the slider by going to Admin Panel > Appearance > Customize > Home sections Options > Slider Section Setting and enable the slider .
Here you can set the slider in two available options. You can either set as the banner image or the slider that sides showing more images . If you chose to set from slider then you can set by choosing the category and if you select this option then make sure to upload the image in featured image section of individual post that is assigned to that category which is chosen to display in the slider .
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