Hello,
Go to Theme Options > Export/Import > Export all options in files then activate the child theme and Import this file (make sure that the header builder is enabled for the child-theme http://prntscr.com/pkx2tu ).
Also, our developers are working on a new feature that will allow export/import settings of the header builder only, and you will be able to install the own settings of the header on other sites, which use XStore, in a few clicks.
If you have any feature requests and suggestions, please post them here – https://www.8theme.com/forums/xstore-wordpress-support-forum/xstore-features/
Regards