Hello, @Linda,
I have debugged your site and found the issue.
1) I activate the parent theme and the header is gone then I again activate the child theme the header appears.
2) Your child theme is creating the issues so please first download it and then delete the child theme.
3) Create the header again and then check back to your site after clearing the browser cache.
4) Then create the child theme again if you want to use it and you can copy and paste the Customize code from the downloaded Child Theme to the new one, one by one.
I made a video for you here is the link to the video for a better reference: https://streamable.com/w0juil
I hope your issue will be resolved.
Regards 8Theme Team.