Hi Ammar, I’m sorry but this is not possible within the theme possibilities.
The theme is made to work with the header, if you remove it, all the height and distances will not work, and you will have problems with the menu positioning and content overlapping.

Options not covered by theme functionalities require custom coding, which is not part of the theme support service, as per contract

https://themeforest.net/page/item_support_policy

Now, as matter of fact, removing a header from a single post is easily achievable via CSS.

To do it, add this code in your custom css of the customizer

.postid-123 .qt-pageheader {display: none;}

Of course replace please 123 with the real ID of your post.

But then, please remember that if you have the sticky header enabled, you will for sure experience design issues on such pages.

Also, please remember that, basing on the Envato support terms, this customization is not part of the service, and we cannot help you if you experience related design glitches.

As matter of fact, customizations of the code are not supported because they can trigger a cascade of subsequent problems, kind of if you put a more powerful engine on a car, it will run faster, but all the other systems as the brakes won’t be fitting the functional change, and you will probably have to do a more complex work than the specific change itself.

Thanks for your kind collaboration and understanding
best regards
Igor

Hello Ammar, I think that probably by now you don’t need further help on this, and I can close the topic, in this case no further action is required, otherwise please let me know.
Thanks and have a nice day!
Igor