Can’t Change ‘Default Kit’ template header

The Blog is using the ‘Default Kit’ template. However, I need to change the header that it’s using, which doesn’t match the rest of the headers throughout the site–it’s not editable.

Looking at the ‘Default Kit’ > Site Settings > Layout Settings > Default Page Layout is ‘Theme’.

So at this point, I’m not sure where to go from here to edit the ‘Default Kit’ header to match the rest of the site.

Thank you.